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The strain DAU334T, which was obtained from samples of sea water and sediments collected from the East Sea in the Republic of Korea, is a rod-shaped, Gram-stain-negative bacterium. It is facultative and positive for the oxidase and catalase enzymes. Based on the analysis of 16S rRNA sequences, it was determined that strain DAU334T had the highest degree of similarity to several strains of Shewanella species, i.e., S. schlegeliana HRKA1T (99%), S. halifaxensis HAE-EB4T (99%), S. pneumatophori SCRC-2738T (99%), S. sairae SM2-1T (99%), and S. marinintestina IK-1T (1419/1440, 99%), respectively. The complete genome sequence consisted of one contig with 4 343 646 bp, and the genome G+C content was 43.12%. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) between strain DAU334T and its closest relatives were 77.85‒71.10, 82.14‒67.07, and 22.60‒19.70%, respectively. The major fatty acids (>10%) of strain DAU334T were iso-C13:0 and Summed feature 3 (C16:1 w7c and/or C16:1 w6c). The respiratory quinones were ubiquinone 7 (Q7), ubiquinone 8 (Q8), menaquinone 7 (MK-7), menaquinone 8 (MK-8), methylated menaquinone 7 (MMK-7), and an unidentified one. According to the results of polyphasic analyses, the strain DAU334T belongs to a novel species within the genus Shewanella, for which the name Shewanellayoungdeokensis sp. nov. (type strain DAU334T = KCTC 72428T = JCM 35745T = KCCM 43479T) is proposed. [ABSTRACT FROM AUTHOR]

Dokdo is an island located in the easternmost part of Korea, which has high levels of biodiversity of birds and fish, especially marine invertebrates. However, the biodiversity of microalgae, especially diatoms (Bacillariophyta), is relatively unknown, despite their ecological importance as primary producers of the marine food web and bioindicators of environmental conditions associated with climate change. To understand the biodiversity of seaweed-associated diatoms from Dokdo, we collected macroalgae present at a depth 5–15 m by SCUBA diving on 17 October 2017. There were a large number of diatoms (over 130 species), even though it was a one-time survey. As it includes too many taxa to cover at once, voucher flora for other taxonomic groups will be provided through the continuous serial papers. This is the first series of seaweed-associated diatoms, with 26 species belonging to the subphyla Melosirophytina and Coscinodisophytina, and the class Mediophyceae. Among these, seven species including one new taxon were reported for the first time in Korea, which, along with the geopolitical characteristics of the survey area, proved that there is no domestic interest in seaweed-related diatoms. In particular, the appearance of species that have been reported in subtropical waters, such as the order Ardissoneales, requires continuous monitoring of marine seaweed-associated diatoms to confirm whether their colonization in Dokdo waters was due to climate change or species-specific water temperature tolerance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Over the past few years, sudden high swells (SHSs) have often occurred on the east coast of the Korean Peninsula (KP), especially during the winter season, causing many casualties and considerable property damage. High waves can be generated suddenly even in the absence of strong winds, sweeping away unsuspecting people on breakwaters or causing damage to properties such as ports and fish farms located on coasts. In this study, we developed a detection and warning system for SHSs on the KP's east coast. First, we developed a method for separating waves into the wind sea and swell components based on one-dimensional wave spectra, wind speed, wind direction, and mean wave direction data obtained from coastal buoys. Using the calculated significant wave height difference between swells and wind seas, as well as wind speed, we developed a SHS alert system with three levels: "Attention," "Watch," and "Warning." This system successfully detected three recent swell events on the east coast of the KP. Applying this system to an operational wave prediction model, it successfully issued an alert 72 h before the SHS reached the coast. The proposed system can provide consistent quantitative forecast information that can greatly contribute to preventing casualties and property damage caused by SHSs. [ABSTRACT FROM AUTHOR]

Dokdo Island's diverse marine ecosystem requires long-term monitoring to understand the effects of rapid environmental changes, such as global warming, on macrobenthos species and communities. Current studies are often short-term and limited, highlighting the need for extended research to predict future changes to ecosystems. This study analyzed the environmental variables influencing macrobenthos through long-term monitoring. In total, 511 species (spp./23.4 m2) were identified with an abundance of 1709.9 individuals/m2 and a diversity of 2.9. Since 2020, there has been a decline in both the number of species and diversity, attributed to changes in sediment composition, particularly an increase in gravel and sand. The dominant species include the crustacean Abludomelita denticulata (17.6%), the polychaete Haplosyllis spongiphila (6.8%), the bivalve Glycymeris munda (5.6%), the polychaete Opisthodonta uraga (5.3%), and the bivalve Limatula japonica (3.8%). The macrobenthos community differs each year, as the dominant species G. munda has decreased in abundance since 2022 and L. japonica since 2021. Depth and gravel sediment strongly correlated with community variation. Site-specific analysis also showed significant differences, with depth, bottom temperature, and sediment composition as the influencing factors. These species thrive in cold water but their abundance declines with an increase in temperature. Continuous long-term monitoring is essential to understand and protect the Dokdo ecosystem amid rapid environmental changes. Long-term monitoring studies have revealed more species than have short-term studies, showing annual and site-specific environmental changes, including sediment erosion and bottom temperature increases. These changes have affected macrobenthos diversity, abundance, and community composition, necessitating ongoing research to determine the persistence of these trends and to protect the ecosystem. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigated how different fish species are distributed in the sea based on where they are relative to the oceanic current region and how deep the water is. Researchers collected fish samples over four seasons from May 2018 to March 2019 along the coasts of the East Sea in Korea. They used special commercial gill nets to catch the fish at different depths, ranging from shallow to deeper waters. Overall, they found 73 different fish species and collected over 6000 specimens. Depending on the oceanic current region, they found different fish species in each study site. For example, in one area called Ayajin, they mostly found fish like blackfin flounder (Glyptocephalus stelleri), Pacific cod (Gadus macrocephalus) and mailclad sculpin (Icelus cataphractus). In another area called Hupo, different fish species were more common, such as blackfin flounder, Sohachi flounder (Cleisthenes pinetorum), and flathead flounder (Hippoglossoides dubius). The researchers also noticed that the types of fish varied depending on how deep the water was. This study helps us understand how fish populations change in different parts of the sea based on the oceanic current region and at different depths. This study assessed variations in demersal fish assemblages with respect to the study site and water depth. Seasonal samplings from May 2018 to March 2019 were conducted along the northern (Ayajin, Goseong) and southern (Hupo, Uljin) sites of the East Sea off the Korean coast, using commercial gill nets. Samples were collected at depths of ~50, ~80, ~150 m across the study sites, with concurrent monitoring of water column structures. A total of 73 species and 6250 specimens were collected. Distinctive fish species compositions were observed according to the study site and depth. Although Glyptocephalus stelleri was the most abundant fish species in both Ayajin and Hupo, Gadus macrocephalus, Icelus cataphractus, and Alcichthys elongatus were most predominant in Ayajin, whereas Cleisthenes pinetorum, Hippoglossoides dubius, and Gymnocanthus herzensteini were more prevalent in Hupo. In terms of depth layer, in Ayajin, G. stelleri dominated in both intermediate and deeper layers, with Hemilepidotus gilberti, A. elongatus, Enophrys diceraus common in shallower depths. Conversely, in Hupo, G. stelleri, C. pinetorum, and A. nadeshnyi dominated across all depth layers, whereas Dasycottus setiger and G. herzensteini dominated in deeper and shallower depths, respectively. Significant influences of the study site and water depth on fish assemblage structures were observed due to variations in water temperature at the seasonal thermocline boundary. [ABSTRACT FROM AUTHOR]

The decline in walleye pollock (Gadus chalcogrammus) stocks in Korean waters is a major concern for fishery conservation and management. However, the causes and mechanisms of this collapse remain unclear. This study investigated the complex dynamics influencing the abundance of walleye pollocks in the East Sea of Korea over several decades, by analyzing data from long-term changes in biological factors including composition of length and sex, catch, and oceanographic condition. Prior to the mid-1980s, the catch ratio of juveniles was higher than that of adults, with a higher proportion of females in both juvenile and adult catches compared to males. Especially, high fishing pressure on female individuals can be an important factor contributing to declining reproduction. Consequently, after the mid-1980s, there was a sudden decline in juvenile pollock catches. In the late 1980s, there was a rapid increase in sea surface temperature (SST) in the spawning grounds, resulting in a decrease in both the duration of suitable temperature for spawning and the regional proportion for suitable spawning conditions. Consequently, the decline in pollock stocks after the late 1980s due to overfishing of pollock in the mid-1980s was further exacerbated by the effects of SST warming after the late 1980s. These findings highlight the impact of overfishing and environmental factors on pollock stocks and indicate the need for appropriate fishery management practices to ensure the sustainable use of fishery resources. [ABSTRACT FROM AUTHOR]

Dokdo is an island located in the easternmost part of Korea, which has high levels of biodiversity of birds and fish, especially marine invertebrates. However, the biodiversity of microalgae, especially diatoms (Bacillariophyta), is relatively unknown, despite their ecological importance as primary producers of the marine food web and bioindicators of environmental conditions associated with climate change. To understand the biodiversity of seaweed-associated diatoms from Dokdo, we collected macroalgae present at a depth 5–15 m by SCUBA diving on 17 October 2017. There were a large number of diatoms (over 130 species), even though it was a one-time survey. As it includes too many taxa to cover at once, voucher flora for other taxonomic groups will be provided through the continuous serial papers. This is the first series of seaweed-associated diatoms, with 26 species belonging to the subphyla Melosirophytina and Coscinodisophytina, and the class Mediophyceae. Among these, seven species including one new taxon were reported for the first time in Korea, which, along with the geopolitical characteristics of the survey area, proved that there is no domestic interest in seaweed-related diatoms. In particular, the appearance of species that have been reported in subtropical waters, such as the order Ardissoneales, requires continuous monitoring of marine seaweed-associated diatoms to confirm whether their colonization in Dokdo waters was due to climate change or species-specific water temperature tolerance.

Background: The Laophontidae is a very large and diverse family containing more than 320 species and 74 genera in the Harpacticoida. According to records published until recently, 25 species of 12 genera of Laophontidae were reported to appear in Korean waters. The most common laophontid species in Korean waters is Paralaophonte congenera (Sars, 1908). During research on the meiobenthic community in the subtidal zone near the Korean coast in the East Sea, we found an undescribed genus of the Laophontidae family. The character traits of this undescribed specimen of the Laophontidae family do not match any existing genus. New information: Herein, a new genus of the interstitial marine benthic copepods family Laophontidae T. Scott, 1905 is described from the subtidal zone near Hupo Harbour on the east coast of Korea. This genus was named Strictlaophonte gen. nov. and has been classified into the family Laophontidae. This was based on the presence of seven segmented female antennules, reduced antennary exopod, first endopodal segments having no inner setae from the second leg to the fourth leg and P5 with a distinct exopod that is not fused at the basis. The distinguishing features of Strictlaophonte gen. nov. are P5 exopod having only four setae, the P1 exopod having two segments and the antenna exopod having four setae. In particular, this new genus has unique characteristics in that the caudal rami are very tightly attached to each other. [ABSTRACT FROM AUTHOR]

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.

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.

Dokdo Island’s diverse marine ecosystem requires long-term monitoring to understand the effects of rapid environmental changes, such as global warming, on macrobenthos species and communities. Current studies are often short-term and limited, highlighting the need for extended research to predict future changes to ecosystems. This study analyzed the environmental variables influencing macrobenthos through long-term monitoring. In total, 511 species (spp./23.4 m2) were identified with an abundance of 1709.9 individuals/m2 and a diversity of 2.9. Since 2020, there has been a decline in both the number of species and diversity, attributed to changes in sediment composition, particularly an increase in gravel and sand. The dominant species include the crustacean Abludomelita denticulata (17.6%), the polychaete Haplosyllis spongiphila (6.8%), the bivalve Glycymeris munda (5.6%), the polychaete Opisthodonta uraga (5.3%), and the bivalve Limatula japonica (3.8%). The macrobenthos community differs each year, as the dominant species G. munda has decreased in abundance since 2022 and L. japonica since 2021. Depth and gravel sediment strongly correlated with community variation. Site-specific analysis also showed significant differences, with depth, bottom temperature, and sediment composition as the influencing factors. These species thrive in cold water but their abundance declines with an increase in temperature. Continuous long-term monitoring is essential to understand and protect the Dokdo ecosystem amid rapid environmental changes. Long-term monitoring studies have revealed more species than have short-term studies, showing annual and site-specific environmental changes, including sediment erosion and bottom temperature increases. These changes have affected macrobenthos diversity, abundance, and community composition, necessitating ongoing research to determine the persistence of these trends and to protect the ecosystem.

Dokdo, a volcanic island located in offshore waters, is significantly influenced by various currents and the island effect resulting from upwelling events. Despite these factors, there is a limited understanding of the seasonal changes in phytoplankton populations and their relationship with the environmental factors in the waters around Dokdo, even during dramatic shifts in phytoplankton dynamics. We focused on seasonal oceanographic features over three years (2018, 2019, and 2020) to understand the phytoplankton community structure and seasonal species succession. Winter, characterized by thorough mixing, results in high nutrient levels, leading to increased phytoplankton biomass. The dominance of the large-sized diatom Chaetoceros spp. contributes to relatively low diversity (H': 1.14 ± 0.31). In contrast to the typical coastal waters, spring exhibits dominance by the small nano-flagellates and Cryptomonas spp. associated with a lack of surface nutrients due to increased water temperature. Summer, characterized by strong stratification, shows low phytoplankton biomass but high Chl. a concentrations, possibly influenced by picoplankton and the emergence of dinoflagellates, such as Gyrodinium sp. and Katodinium sp., which increases diversity (H': 2.18 ± 0.28). In autumn, there is typically a phytoplankton bloom, but in 2019, an unusually low biomass occurred. This was likely due to the intrusion of deep, cold water from the bottom and low-salinity Changjiang diluted water (CDW) from the surface, increasing the water's stability. This, in turn, led to nutrient depletion, contributing to a rise in diversity (H': 1.14 ± 0.31). These environmentally complex waters around Dokdo result in a distinct pattern of biodiversity indices, with the highest in summer and the lowest in winter, differing from typical temperate waters. In conclusion, this research highlights the substantial influence of distinctive oceanographic features and nutrient dynamics on the phytoplankton biomass and biodiversity in the Ulleung Basin and Dokdo region. Understanding these patterns is vital for the effective management of marine ecosystems and fisheries resources, emphasizing the necessity for continued long-term monitoring in the vicinity of the Dokdo area. [ABSTRACT FROM AUTHOR]

Ocean ventilation is a key mechanism for transporting anthropogenic CO2 (CANTH) from the ocean surface toward its interior. We investigated the link between ocean ventilation and CANTH increase in the East Sea using data from surveys conducted in 1992, 1999, 2007, and 2019. Between 1992 and 1999, the East Sea Intermediate Water (300−1,500 m) accumulated CANTH at a rate of 0.3 ± 0.1 mol C m−2 yr−1. However, in the subsequent period (1999−2007) this rate decreased to <0.1 ± 0.1 mol C m−2 yr−1. There was a resurgence in the CANTH increase rate between 2007 and 2019, reaching 0.4 ± 0.1 mol C m−2 yr−1. The East Sea Intermediate Water ventilation changes, inferred from the changes in water column O2 level and the Arctic Oscillation‐driven winter surface temperature in the deep water formation region, were responsible for the periodic decline and recovery in CANTH increase. Plain Language Summary: Ocean ventilation plays a crucial role in transporting anthropogenic CO2 from the surface toward the deep ocean interior. In the East Sea, demonstrating a direct causal relationship between ocean ventilation and anthropogenic CO2 uptake has remained elusive because of limited observational evidence. To address this knowledge gap, we conducted direct measurements of carbon parameters during four surveys in the East Sea that together spanned nearly three decades (1992, 1999, 2007, and 2019). Our investigation revealed a cyclical pattern of waxing and waning in the rate of anthropogenic CO2 increase within the East Sea over the past three decades. Significantly, we demonstrated that fluctuations in the ventilation of the East Sea were the primary driving force behind the decadal changes in anthropogenic CO2 increase. Furthermore, our research unveiled a potential connection between the periodic fluctuations in surface temperature linked to the Arctic Oscillation and variations in East Sea ventilation. Our findings shed light on the intricate dynamics between ocean ventilation, winter sea surface temperature patterns, and CO2 uptake in the East Sea. Key Points: The rate of anthropogenic CO2 increase in the East Sea showed cyclic trendsThe cyclic trends of anthropogenic CO2 increase were linked to the Arctic OscillationOur findings shed light on changes in anthropogenic CO2 uptake and transport by the global ocean in response to climate variations [ABSTRACT FROM AUTHOR]

This study assessed variations in demersal fish assemblages with respect to the study site and water depth. Seasonal samplings from May 2018 to March 2019 were conducted along the northern (Ayajin, Goseong) and southern (Hupo, Uljin) sites of the East Sea off the Korean coast, using commercial gill nets. Samples were collected at depths of ~50, ~80, ~150 m across the study sites, with concurrent monitoring of water column structures. A total of 73 species and 6250 specimens were collected. Distinctive fish species compositions were observed according to the study site and depth. Although Glyptocephalus stelleri was the most abundant fish species in both Ayajin and Hupo, Gadus macrocephalus, Icelus cataphractus, and Alcichthys elongatus were most predominant in Ayajin, whereas Cleisthenes pinetorum, Hippoglossoides dubius, and Gymnocanthus herzensteini were more prevalent in Hupo. In terms of depth layer, in Ayajin, G. stelleri dominated in both intermediate and deeper layers, with Hemilepidotus gilberti, A. elongatus, Enophrys diceraus common in shallower depths. Conversely, in Hupo, G. stelleri, C. pinetorum, and A. nadeshnyi dominated across all depth layers, whereas Dasycottus setiger and G. herzensteini dominated in deeper and shallower depths, respectively. Significant influences of the study site and water depth on fish assemblage structures were observed due to variations in water temperature at the seasonal thermocline boundary.

The East Sea has a vital position for maritime powers worldwide and is a crucial point of strategic competition for significant countries. Currently, the East Sea is where many fierce disputes over sovereignty, sovereign rights, and jurisdiction occur between coastal countries because the views and interests of each side are far apart, and they need help finding a consensus on how to solve the problem. The US interests in the East Sea include diverse interests in freedom of navigation, economics, politics, military, and security. The article aims to systematically analyze and explain the US policy towards the East Sea issue since the US Administration announced the Pivot to Asia-Pacific strategy. The US foreign policy towards the East Sea has changed in the direction of increased US involvement in response to rising tensions over disputes, especially towards increased interests of China in this region. Although the United States does not take sides in sovereignty claims, it nevertheless increases its involvement in the issue, focusing on peaceful control of claims and resolving disputes through peaceful negotiation measures.

Abstract Ocean ventilation is a key mechanism for transporting anthropogenic CO2 (CANTH) from the ocean surface toward its interior. We investigated the link between ocean ventilation and CANTH increase in the East Sea using data from surveys conducted in 1992, 1999, 2007, and 2019. Between 1992 and 1999, the East Sea Intermediate Water (300−1,500 m) accumulated CANTH at a rate of 0.3 ± 0.1 mol C m−2 yr−1. However, in the subsequent period (1999−2007) this rate decreased to

The shape and structure of otoliths play a vital role in studying fish populations because otolith shape indices are often applied to discriminate fish species. This study focused on examining inter- and intra-specific variations in otolith shape and size among three species of rockfish (Sebastes inermis, Sebastiscus marmoratus, and Sebastes zonatus) collected from the Dokdo and Ulleungdo regions of the East Sea in Korea. A total of 35 S. inermis specimens, 19 S. marmoratus specimens, and 59 S. zonatus specimens were collected between April 2021 and August 2022. The otolith shape was visualized using wavelet coefficients in the shapeR package. Otolith size indices, such as length, width, perimeter, and area, and shape indices, including form factor, aspect ratio, ellipticity, circularity, roundness, rectangularity, and squareness, were calculated for each species. Otolith size and shape indices significantly differed among the three rockfish species (p< 0.05). Compared with the other two species, S. marmoratus possessed more elongated otoliths, whereas S. zonatus had the largest otolith area, perimeter, and length. Average shape analysis based on wavelet coefficients revealed significant differences in otolith shape, particularly on the rostrum and posterior sides. A canonical analysis of principal components (CAP) confirmed the complete separation of otolith shapes among the three rockfish species, with 92.5% of the variation explained by the first axis (CAP1). The findings of this study enhance our understanding of the fish species in the Korean East Sea.

The East Sea has a vital position for maritime powers worldwide and is a crucial point of strategic competition for significant countries. Currently, the East Sea is where many fierce disputes over sovereignty, sovereign rights, and jurisdiction occur between coastal countries because the views and interests of each side are far apart, and they need help finding a consensus on how to solve the problem. The US interests in the East Sea include diverse interests in freedom of navigation, economics, politics, military, and security. The article aims to systematically analyze and explain the US policy towards the East Sea issue since the US Administration announced the Pivot to Asia-Pacific strategy. The US foreign policy towards the East Sea has changed in the direction of increased US involvement in response to rising tensions over disputes, especially towards increased interests of China in this region. Although the United States does not take sides in sovereignty claims, it nevertheless increases its involvement in the issue, focusing on peaceful control of claims and resolving disputes through peaceful negotiation measures. [ABSTRACT FROM AUTHOR]

This study reports a rare case of failing incipient subduction found in the East Sea (Japan Sea), a back‐arc basin in the western circum‐Pacific, where an opposing pair of incipient‐diffuse subduction margins competes to attain self‐sustainability. Seismic reflection analysis of the post‐4 Ma structural components around the western East Sea margin revealed three juxtaposed compressional neotectonic components: (a) the Ulleung Major Thrust, (b) the Ulleung Syncline, and (c) the East Korean Thrust Belt. The Ulleung Major Thrust, marked by the NS‐elongated west‐dipping reverse tri‐shear zone along the continent–back‐arc transition boundary, is interpreted as an embryonic subduction interface that began to guide the underthrust of the Ulleung back‐arc crust below the Korean continental block. With the growth of the Ulleung Major Thrust, the crustal downbuckle on the western end of the Ulleung Basin became progressively asymmetric and formed the Ulleung Syncline, a proto‐trench. Underthrusting of the Ulleung Basin crust induced regional uplift over the eastern Korean margin, accommodated by arrays of east‐dipping thrust faults referred to as the East Korean Thrust Belt. The east‐upward thrust movements formed NS‐elongated thrust‐bounded sedimentary basins, classified as piggyback basins. The subduction initiation on the western East Sea margin appears destined to fail, because a convergent proto‐plate boundary is now nucleating on its opposing side. However, lines of evidence, such as marine terraces and frequent compressional earthquakes on Quaternary faults along the eastern Korean margin imply that the subduction initiation on the western East Sea is failing but has not yet failed. Key Points: We investigated a failing subduction initiation in an opposing pair of incipient‐diffuse subduction systems of the East Sea (Japan Sea)Incipient subduction system comprises an immature subduction interface, a proto‐trench, and a thrust fault belt on the overriding crustSubduction initiation on the western East Sea margin is not yet failed considering uplifting marine terraces and seismicity [ABSTRACT FROM AUTHOR]

The first specimen (54.8 mm standard length) of Ernogrammus zhirmunskii Markevich & Kharin, 2011, belonging to the family Stichaeidae, was recorded in Dokdo, East Sea, Korea on July 26, 2021. This species was characterized by a single ventral lateral-line canal from the posterior margin of the pelvic-fin base extending to the anus and one or two rigid spines on the posterior part of the anal fin. This species is similar to Ernogrammus hexagrammus and Ernogrammus walkeri but differs in the number of ventral lateral-line canal present, with E. zhirmunskii consisting of one (unpaired) ventral lateral-line canal compared to other two Ernogrammus species, which have a pair of parallel ventral lateral-line canal. For further analysis of species identification, a partial gene sequence from the mitochondrial DNA cytochrome oxidase subunit I (554 bp) of E. zhirmunskii was obtained for the first time. This study documents the first record of E. zhirmunskii in Korean waters and proposes the new Korean name of ‘Il-gob-julbe-do-la-chi’ for the species.

In 2021 the East Sea experienced its highest July sea level (65.09 cm), as well as the highest July sea surface and atmospheric temperatures, in the 29 years between 1993 and 2021. We present several methodologies to identify the more important causes of sea level change (SLC) in a semi-enclosed sea and explore the critical fluctuation of ocean mass transport divergence during a period of rapid sea level rise. Based on satellite altimeter data in the East Sea, the SLC, as reflected in the absolute dynamic topography (ADT), which is the ADT difference between the last and first days of a month, was 7.18 cm in July 2021. This may reflect a combination of oceanic and atmospheric factors: ocean heat transport divergence among the Korea, Tsugaru, and Soya Straits was found to contribute 2.32 cm of SLC, atmospheric heat flux at the sea surface contributed 2.87 cm of SLC, and mass divergence (including errors) accounted for 1.98 cm of SLC. The monthly mean sea level (ADT) variation in the East Sea should be examined in terms of the oceanic and atmospheric fluxes, and the SLC sources can additionally be divided into heat and others (mass + errors). The proportional contribution of heat to SLC from 1994 to 2021 was 97.4%. Although the contributions of mass and errors were small, there were substantial temporal fluctuations, as their standard deviation reached up to 96.7% of that of SLC in ADT. In the near future, a more precise analysis of the contributions of mass and errors to SLC is required.

Dietary habits and inter-specific differences in resource use among six commercial fish species, Chelidonichthys spinosus, Cleisthenes pinetorum, Glyptocephalus stelleri, Hexagrammos otakii, Lophius litulon, and Sebastes schlegelii, collected from the southern coast of the East Sea, Korea, were analyzed using stomach content and stable isotope analyses. Teleosts were the main prey items for C. pinetorum and L. litulon, while both crabs and teleosts contributed to the diets of C. spinosus and S. schlegelii. Glyptocephalus stelleri mainly consumed polycheates and carid shrimps, and H. otakii mostly ingested crabs. The composition of prey items was significantly different in the diets of the six fish species. Further, carbon (δ13C) and nitrogen (δ15N) stable isotope values were significantly different among the six species, indicating different trophic positions. L. litulon, C. pinetorum, and S. schlegelii had narrow niches, whereas C. spinosus, G. stelleri, and H. otakii had relatively wider niches. This study demonstrated differences in patterns of food resource use among the six fish species that were categorized into two patterns of resource use according to their main prey items: diet diversity, trophic niche width, and trophic position. These results could contribute to the understanding of trophic relationships among fish species inhabiting the East Sea, Korea. [ABSTRACT FROM AUTHOR]

Three long marine cores collected from the southwestern part of the Ulleung Basin in the East Sea were investigated in terms of chronology, from the middle Pleistocene to Holocene. We propose an age–depth model in cores 19ESDP-101, 19ESDP-103, and 19ESDP-104 obtained through precise age data using a suitable statistical method and classified in chronological units according to their accumulation rates. Changes in accumulation rate in cores 19ESDP-103 and 19ESDP-104, located at the entrance to the contact of the Korean Strait and the Ulleung Basin, showed good agreement with glacial and interglacial cycles. Relatively increased accumulation rates are related to ocean currents flowing through the Korea Strait during interglacial periods of Marine Isotope Stage (MIS) 5 and 7. However, core 19ESDP-101 obtained from the Hupo Basin, located in the northern site, showed a high accumulation rate in the glacial periods of MIS 6 and 8. It is interpreted as an increase in the sediment input from the exposed shallow shelf and inland fluvial, despite the fact that ocean currents from the Korea Strait are blocked by the exposed shelf platform as the sea-level falling down. These results show that the continental shelf on the western East Sea has been deposited from various factors related to several sea-level fluctuations from the glacial-interglacial cycle during the middle to late Quaternary. This study contributes to stratigraphic study in the Korean continental shelf environment of the East Sea from the middle Pleistocene to Holocene. [ABSTRACT FROM AUTHOR]

We investigated the trophic relationship between particulate organic matter (POM) and sympatric copepods within the epipelagic zone (~200 m depth) in the East Sea during spring based on stable isotope analysis (SIA). The SIA indicated that interspecific differences in the prey size and vertical segregation of feeding migration range among copepods may promote niche partitioning among sympatric copepods in each region of the subpolar front (SPF). Additionally, our results showed remarkable differences in the copepod community structure and resource utilization across the SPF. The south region of the East Sea showed higher species richness of copepods than the north region, while copepods that fed mainly on POM in the surface and subsurface chlorophyll maximum layers showed smaller body sizes in the south region. These results revealed that the food chain between primary producers and higher trophic levels was longer in the south region than in the north region. Additionally, δ13C and δ15N values of copepods increased gradually with the body size increase whereas δ15N values in the north region showed the reverse trend. Latter results could be attributed to the consumption of deep-layer POM in small copepods. Therefore, we suggest that northward shifts in the distribution of copepods under global warming may decrease energy efficiency in the pelagic ecosystem of the East Sea. [ABSTRACT FROM AUTHOR]

The Ulleung Basin of the East Sea is a biological hotspot, but studies on the macrobenthos therein are lacking. To evaluate the macrobenthos species diversity and community structure in the Ulleung Basin, we conducted a survey from 2017 to 2021. A total of 262 species of macrobenthos was detected by the survey, and the average habitat density was 243 individuals/m2. The average biomass of macrobenthos was 43.7 g/m2, and the average Shannon and Wiener's diversity index was 2.3 (0.69–3.61). The dominant species were the polychaetes Terebellides horikoshii, Chaetozone setosa, Scalibregma inflatum, and Aglaophamus sp. and the bivalvia Axinopsida subquadrata. The community structure of macrobenthos differed according to water depth, and a correlation analysis using environmental variables showed that the community was affected by water temperature, salinity, and dissolved oxygen. The macrobenthic fauna in the Ulleung Basin was greatly influenced by water depth, the sedimentary environment was different, and the dominant species were also different. In addition, there was little seasonal change compared to the East Sea coast. Our findings will facilitate further investigation of benthic ecosystems throughout the East Sea. [ABSTRACT FROM AUTHOR]

The coastal waters of Vietnam are home to a wide diversity of fishes, but the parasite diversity of these potential hosts is much less well characterized. To begin addressing this knowledge gap, we carried out surveys of myxozoan parasites in fishes collected from Nha Trang Bay in Vietnam's East Sea in 2018–2019. Mugilid fishes were collected in March–April 2018, January–February 2019, and November–December 2019, and examined for myxozoans. Myxospores consistent with those of the genus Ellipsomyxa were found in the gall bladder of four mullet species, and we thoroughly characterized those from Planiliza melinoptera. Myxospores were elliptoid and devoid of striation, with a distinct sinuous suture line. Polar capsules were pyriform and oriented toward the poles of the spore. Morphological features were compared to nominal species and this species from Vietnam was distinct. Phylogenetic analysis based on partial small subunit rDNA sequence revealed that broadly, Ellipsomyxa species split into three phylogenetic lineages, and although in some branches there are groupings by host family, habitat or locality, there are no clear phylogenetic patterns. The new species we encountered in P. melinoptera had a close sister relationship with Ellipsomyxa adlardi , with both species part of a larger subclade within the Ellipsomyxa lineage. Despite this phylogenetic similarity, these species were morphologically distinct, and partial large subunit DNA sequences were only 93% similar to each other. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species and we propose the name Ellipsomyxa gordeyi n. sp. [Display omitted] • New species Ellipsomyxa gordeyi n. sp. from Vietnamese waters. • Phylogenetic analysis of Ellipsomyxa species reveals inconsistent patterns. • Genetic analyses are critical for the identification of myxosporean species. [ABSTRACT FROM AUTHOR]

Dokdo, a volcanic island located in offshore waters, is significantly influenced by various currents and the island effect resulting from upwelling events. Despite these factors, there is a limited understanding of the seasonal changes in phytoplankton populations and their relationship with the environmental factors in the waters around Dokdo, even during dramatic shifts in phytoplankton dynamics. We focused on seasonal oceanographic features over three years (2018, 2019, and 2020) to understand the phytoplankton community structure and seasonal species succession. Winter, characterized by thorough mixing, results in high nutrient levels, leading to increased phytoplankton biomass. The dominance of the large-sized diatom Chaetoceros spp. contributes to relatively low diversity (H’: 1.14 ± 0.31). In contrast to the typical coastal waters, spring exhibits dominance by the small nano-flagellates and Cryptomonas spp. associated with a lack of surface nutrients due to increased water temperature. Summer, characterized by strong stratification, shows low phytoplankton biomass but high Chl. a concentrations, possibly influenced by picoplankton and the emergence of dinoflagellates, such as Gyrodinium sp. and Katodinium sp., which increases diversity (H’: 2.18 ± 0.28). In autumn, there is typically a phytoplankton bloom, but in 2019, an unusually low biomass occurred. This was likely due to the intrusion of deep, cold water from the bottom and low-salinity Changjiang diluted water (CDW) from the surface, increasing the water’s stability. This, in turn, led to nutrient depletion, contributing to a rise in diversity (H’: 1.14 ± 0.31). These environmentally complex waters around Dokdo result in a distinct pattern of biodiversity indices, with the highest in summer and the lowest in winter, differing from typical temperate waters. In conclusion, this research highlights the substantial influence of distinctive oceanographic features and nutrient dynamics on the phytoplankton biomass and biodiversity in the Ulleung Basin and Dokdo region. Understanding these patterns is vital for the effective management of marine ecosystems and fisheries resources, emphasizing the necessity for continued long-term monitoring in the vicinity of the Dokdo area.

In March and April 2018, we carried out a survey of myxosporean parasites in coastal fishes collected from Nha Trang Bay in Vietnam's East Sea. Of the 159 fish specimens, 18 fish species were represented, belonging to 10 families. In 8 host species, 7 myxosporean species were found, representing the genera Kudoa and Unicapsula. Two of these species were new to science: Kudoa igori n. sp. from the gallbladder of Longarm mullet Osteomugil cunnesius (Valenciennes, 1836) (prevalence 10%) and Kudoa borimiri n. sp. from skeletal muscles of Longarm mullet and Longfinned mullet Osteomugil perusii (Valenciennes, 1836) (prevalence 30% and 60%, respectively). Vegetative stages were not found. Spores of K. igori n. sp. were small, orbicular to quadrate in apical view, and with four equal valves. In lateral view, spores were shallowly ovoid with a slightly protruding anterior pole. The 4 polar capsules were slightly unequal sizes and were oriented toward the apex of the spore. Dimensions were as follows: spore length 4.56 ± 0.22 (4.18–4.56), thickness 4.42 ± 0.39 (3.55–5.13), width 5.74 ± 0.46 (4.66–6.50), length of biggest polar capsule 1.38 ± 0.14 (1.1–1.65), middle 1.28 ± 0.12 (1.03–1.53), smallest 1.13 ± 0.11 (0.94–1.30), width of biggest polar capsule 1.03 ± 0.14 (0.83–1.4), middle 0.92 ± 0.12 (0.76–1.08), smallest 0.74 ± 0.12 (0.55–0.94). Spores of K. borimiri n. sp. had four equal valves with slightly rounded ends and were quadrate in apical view. In lateral view, spores were broadly deltoid. Four equal-sized polar capsules opened at the apex of the spore. In O. cunnesius, spore dimensions were as follows: length 3.51 ± 0.15 (3.34–3.92), thickness 3.65 ± 0.38 (2.79–4.21), width 4.97 ± 0.37 (4.13–5.97), length of the polar capsules 1.23 ± 0.18 (0.99–1.57), width 0.88 ± 0.07 (0.70–1.00). Overlapping dimensions for K. borimiri n. sp. spores were also found in O. perusii. Other known myxozoan species we encountered were Kudoa thyrsites and Kudoa whippsi, which had not previously been reported from the East Sea and Vietnam. We also encountered Kudoa monodactyli, which had not previously been reported from Nha Trang Bay. In addition, we report 2 additional species, a Kudoa sp. and a Unicapsula sp., that were not attributable to previously described myxozoans and need further investigation to completely characterize. [ABSTRACT FROM AUTHOR]

The chlorophyll-a concentration (CHL) data observed with the ocean color sensors have been widely used in the various studies related to phytoplankton. However, irregularly distributed missing data induced by clouds, a unique nature of optics, can cause large uncertainty, and a solution to this missing issue has been continuously demanded until now. We investigated the applicability of the data interpolating empirical orthogonal function and evaluated the reconstruction results in the southwestern East Sea. A total of 311 decomposed modes were used, showing a coefficient of determination of about 0.86 and a root mean square error of 0.37 mg m−3, compared to the truth data. Overall, it was confirmed that the observed CHL was overestimated compared to the reconstructed CHL when the spatio-temporal average was taken.

Photosynthetic organisms shift the dynamics of surface pCO2 driven by the sea surface temperature change (thermodynamic driver) by assimilating inorganic C from seawater. Here we measured net C uptake in a macroalgal habitat of coastal Korea for two years (2019-2020) and found that the macroalgal habitat contributed 5.8 g C m−2 month−1 of the net C uptake during the growing period (the cooling period, September−May). This massive C uptake changed the thermodynamics-driven seasonal dynamics such that the air−sea equilibrium of pCO2 was pushed into disequilibrium. The surface pCO2 dynamics during the cooling period was mostly influenced by the seasonal decrease in temperature and the proliferation of macroalgae, while the dynamics during the warming period (the stagnant period, June−August) closely followed that predicted based solely on the change in sea surface temperature (thermodynamic driver). In contrast to the phytoplankton-dominated off-shore waters (where phytoplankton populations are large in spring and summer), the impact of coastal macroalgae on surface pCO2 dynamics was most pronounced during the cooling period, when the magnitude of pCO2 change was as much as twice that resulting from temperature change. Our study shows that the distinctive features of the macroalgal habitat—in particular the seasonal temperature extremes (~18°C difference), the active macroalgal metabolism, and anthropogenic nutrient inputs—collectively influenced the seasonal decoupling of seawater and air pCO2 dynamics.

Mixing at the southwestern boundary of the Ulleung Basin (UB) in the Japan/East Sea was examined using combined ship‐based, moored, and quasi‐autonomous observations. These observations revealed strong tidal currents, high‐frequency internal wave packets, and energetic turbulence over the sill connecting the Korea/Tsushima Strait and the UB, especially when a supercritical flow becomes subcritical over the sill. In addition, strong velocity shear associated with the semidiurnal baroclinic tide was found near the bottom, where the bathymetry slope was critical to the semidiurnal tide. Large temperature fluctuations were observed during the subcritical phase of the flow, as hydraulically controlled flow generated internal‐wave packets and energetic turbulence with a turbulent‐kinetic‐energy dissipation rate of ∼ $\sim $10−4 Wkg−1, and a diapycnal diffusivity of ∼ $\sim $10−2 m2s−1. Our analysis suggests that the sill is a hot spot of mixing, which in turn can play an important role in the Japan/East Sea circulation. Plain Language Summary: The Japan/East Sea (JES) is a semi‐enclosed deep marginal sea, connected with the East China Sea, North Pacific Ocean, and Sea of Okhotsk through shallow straits which control water‐mass exchange. This study presents observations of mixing over the sill connecting the northern Korea/Tsushima Strait (KTS) with the southern Ulleung Basin (UB), where the warm and high‐salinity equatorial water carried by the Tsushima Current interacts with southward‐flowing subsurface water‐masses in the JES. Observations reveal that tides, especially semidiurnal tides control mixing over the sill, where intense mixing occurs as supercritical tidal currents in the KTS become subcritical over the sill. Furthermore, strong vertical shears are generated as the barotropic tide transitions to a baroclinic tide over the sill. Our analysis suggests that the sill between the KTS and the UB is a crucial region of water‐mass exchange in the southern JES, and may impact on the entire JES circulation. Enhanced energetic mixing over the sill forms a "mixing hotspot" that produces diapycnal upwelling orders of magnitude greater than the average‐upwelling in the interior, inferred from the analysis of chemical tracers. Key Points: The southern boundary of the Ulleung Basin (UB) in the Japan/East Sea is a "hot spot" for mixing, which impacts water‐mass propertiesIntense turbulent mixing occurs over the sill at the southern UB, when a supercritical flow transforms to a subcritical flowBaroclinic semidiurnal tides boost the mixing above the bottom where the slopes of the bathymetry and the tide raypath are equal [ABSTRACT FROM AUTHOR]

Time- and depth-domain processing procedures were applied to seismic data acquired from shallow coastal areas using limited source-receiver offset ranges. A signal-to-noise ratio improvement strategy was applied in time-domain processing, and migration velocity analysis (MVA) with tomographic inversion was performed at every common image gather domain. Although the source-receiver offset was limited, the seismic image generated by the velocity from MVA represents more transparent reflections compared to the image from applied time processing only, which is likely because the shallow water depth of the survey area might yield a certain range of offsets. The processing procedure applied in this case also focused on the improvement of high-frequency content and removing as many multiples as possible in the time domain. Several small-scale faults and horizons of sedimentary units were well defined by this method. The improvement of the image with an accurate velocity by our method was demonstrated by representing the flattened events in the common image gather and velocity differences between time and depth processing. The final prestack depth migration image generated by our approaches provides refined information to interpreters that reduces uncertainties in geohazard assessments. [ABSTRACT FROM AUTHOR]

The spatial distributions of dissolved lead (Pb) concentrations and stable Pb isotope ratios in the Ulleung Basin, East/Japan Sea, were investigated to identify the Pb source, the behavior of Pb in seawater, and the relationship between Pb isotopes and water masses. The Pb concentrations showed a surface maximum and rapidly decreased with increasing water depth. In the slope area, Pb concentrations increased near the seafloor due to diffusive flux from the sediments. The Pb concentrations in the surface layer were higher than in the Northwest Pacific Ocean and western Philippine Sea due to the proximity and downwind location of the sampling site from a Pb source area. The bottom Pb concentrations were lower in the study area than in the open ocean, indicating a higher scavenging rate due to the presence of well-developed bottom boundary layers from the continental slope to the basin. The Pb isotope ratios obtained from the continental slope and basin area were relatively constant among water masses. The Pb isotope ratios in the surface layer were similar to those of coal from northern China, which may indicate Pb supply from coal combustion in China. Meanwhile, Pb in the bottom water had a similar isotopic signature to Russian ore deposits and coal, indicating that bottom Pb is associated with thermohaline circulation in the East/Japan Sea. The Pb isotope ratios of the intermediate layer were constant across the depths of East Sea Central Water (ESCW) and were similar to aerosols measured previously (in 2003–2004) around Ulleung Island, which may indicate the timing of ESCW formation. [ABSTRACT FROM AUTHOR]

This article analyses the activities of pirates and measures to prevent piracy during the Nguyen Dynasty (Vietnam) in the Central Sea in the nineteenth century. The research is based on an analysis of original sources compiled by historians of the Nguyen Dynasty. The results show that piracy was quite common in the East Sea in the nineteenth century. Pirates originated mainly from neighbouring countries such as China, Japan and Indonesia. The study also shows that the Nguyen Dynasty applied many measures to prevent piracy and it achieved practical results. The results of the research not only contribute to clarifying the history of maritime security in the nineteenth century but also suggest recommendations to ensure maritime security in the East Sea nowadays. [ABSTRACT FROM AUTHOR]

In recent years, as human casualties and property damage caused by hazardous waves have increased in the East Sea, precise wave prediction skills have become necessary. In this study, the Simulating WAves Nearshore (SWAN) third-generation numerical wave model was calibrated and optimized to enhance the accuracy of winter storm wave prediction in the East Sea. We used Source Term 6 (ST6) and physical observations from a large-scale experiment conducted in Australia and compared its results to Komen’s formula, a default in SWAN. As input wind data, we used Korean Meteorological Agency's (KMA’s) operational meteorological model called Regional Data Assimilation and Prediction System (RDAPS), the European Centre for Medium Range Weather Forecasts’ newest 5th generation re-analysis data (ERA5), and Japanese Meteorological Agency's (JMA’s) meso-scale forecasting data. We analyzed the accuracy of each model’s results by comparing them to observation data. For quantitative analysis and assessment, the observed wave data for 6 locations from KMA and Korea Hydrographic and Oceanographic Agency (KHOA) were used, and statistical analysis was conducted to assess model accuracy. As a result, ST6 models had a smaller root mean square error and higher correlation coefficient than the default model in significant wave height prediction. However, for peak wave period simulation, the results were incoherent among each model and location. In simulations with different wind data, the simulation using ERA5 for input wind datashowed the most accurate results overall but underestimated the wave height in predicting high wave events compared to the simulation using RDAPS and JMA meso-scale model. In addition, it showed that the spatial resolution of wind plays a more significant role in predicting high wave events. Nevertheless, the numerical model optimized in this study highlighted some limitations in predicting high waves that rise rapidly in time caused by meteorological events. This suggests that further research is necessary to enhance the accuracy of wave prediction in various climate conditions, such as extreme weather.

Abstract Mixing at the southwestern boundary of the Ulleung Basin (UB) in the Japan/East Sea was examined using combined ship‐based, moored, and quasi‐autonomous observations. These observations revealed strong tidal currents, high‐frequency internal wave packets, and energetic turbulence over the sill connecting the Korea/Tsushima Strait and the UB, especially when a supercritical flow becomes subcritical over the sill. In addition, strong velocity shear associated with the semidiurnal baroclinic tide was found near the bottom, where the bathymetry slope was critical to the semidiurnal tide. Large temperature fluctuations were observed during the subcritical phase of the flow, as hydraulically controlled flow generated internal‐wave packets and energetic turbulence with a turbulent‐kinetic‐energy dissipation rate of ∼10−4 Wkg−1, and a diapycnal diffusivity of ∼10−2 m2s−1. Our analysis suggests that the sill is a hot spot of mixing, which in turn can play an important role in the Japan/East Sea circulation.

The East/Japan Sea (ES) is regarded as a natural laboratory for predicting future changes in the global Meridional Overturning Circulation (MOC) under warming climates, as the ES MOC (EMOC) changes rapidly in comparison with the global MOC. Specifically, intermediate and deep-water masses of the ES are formed in its northern reaches via wind-driven subduction of surface water, and convection from the surface to deep layers during the winter. Accordingly, it is important to investigate the variation of winter sea surface temperatures (SSTs) for characterizing and predicting the EMOC; however, global SST products must be corrected and optimized for the ES, as they fail to incorporate the local marginal sea conditions. Here, a warm bias in cold SST was identified for three SST products, such as optimally interpolated sea surface temperatures (OISSTs), microwave SSTs, and operational SST and sea ice analysis products, suggesting the potential usefulness of a correction method incorporating Argo float data. When comparing OISSTs with 5 m temperature estimates from Argo float data during 2000–2020, under the assumption that the mixed layer depth is deeper than 8 m, a nearly normalized histogram of biases was produced, and the robust warm bias (mean = 0.9°C) was detected in the range of relatively cold SSTs (-2°C to 10°C), yet no significant bias in warm SSTs (> 10°C) was found. To minimize the warm bias in cold SSTs, OISSTs were corrected with an inverse 4th-order polynomial fitting method. Subsequently, the mean bias between the corrected SSTs and top depth temperatures of Argo float data was significantly reduced to less than 0.1°C. Moreover, the warm bias of cold SSTs resulted in severe underestimations of the outcropping area colder than 1°C over the northern region, as well as the occurrence period of 1°C to 5°C SSTs in the north-western ES. These results highlight the importance of local bias correction for SST products, and it is expected that the newly suggested correction method will improve model predictions of EMOC change by enhancing SST data quality in the northern ES.

South Korea intends to install a floating offshore wind farm (FOWF) with a capacity of 9 GW off its east coast by 2030. This article seeks to apply contingent valuation, analyze households' willingness to pay (WTP) for this installation quantitatively, and derive some implications. Data on WTP were collected through a survey of 1000 households across the country. WTP was induced through the one-and-one-half-bound question method, and positive WTP and zero WTP were analyzed together through the spike model. Statistical significance was secured for the main estimation results of the model. The average WTP was KRW 3302 (USD 2.58) per household per month, which was about 7.5% of the average electricity bill. In addition, it was found that the respondents' education level, income level, residence, and perceptions had a significant effect on their WTP. Finally, along with five challenges faced by the FOWF identified during the survey process, possible solutions to these are presented. For example, the most important challenge was acceptance by fishers. [Display omitted] • South Korea intends to install a floating offshore wind farm. • The households' willingness to pay (WTP) for this installation is examined. • A contingent valuation survey of 1000 randomly sampled households was performed. • Monthly household WTP was KRW 3302 (USD 2.58). [ABSTRACT FROM AUTHOR]

We studied the Quaternary incised fills drilled at the northern Yangsan Fault having multiple deformation histories since Late Cretaceous or Paleogene to determine tectonic influence on development of incised valley and its sedimentation. Incised valley fills were deposited during and after the Last Glacial Maximum and are composed of fluvial lag, debris flow deposits interbedded with fluvial sediments, shallow marine sandy deposits, and fluvial sediments from bottom to top. These fills show lateral changes in sediment thickness from 44 to 11.5 m over a short distance of 230 m, implying sediment stacking in a deep and steeply inclined valley. Fluvial lag and debris flow deposits are common in the thalweg of a valley. Despite small drainage basin (195.9 km2), the development of deep incised valley is interpreted to have resulted from fluvial downcutting on erodible basement during sea level fall as a consequence of dense development and fault and fracture networks in the pre-Quaternary rocks caused by multiple movements of Yangsan Fault. With steep gradient, the damaged rocks led to frequent slope failure and forceful accumulation of debris flow deposits on the valley’s axis at the time. In addition, stacking of debris flow deposits resulted in decrease of longitudinal gradient of incised valley, promoting rapid transgression during sea level rise (9 to 7 ka). This resulted in insufficient time for the central basin mud to be accumulated, which explains why the studied fills lack central estuarine mud that is common in incised valleys fills deposited during transgression. [ABSTRACT FROM AUTHOR]

The article provides a perspective of the East Sea in China's naval strategy through Alfred Thayer Mahan's theory of sea power - naval historian of United States. In addition, some new viewpoints have been offered from the current international conditions, which mainly focus on scientific and technical factors, the international context as well as new tactics. On that basis, it points out new geostrategic points to better clarify China's intentions in the East Sea. [ABSTRACT FROM AUTHOR]

We characterized the biogeochemical organic carbon (Corg) cycles in the surface sediment layer of the Ulleung Basin (UB) of the East Sea. The total oxygen uptake (TOU) rate and the diffusive oxygen uptake (DOU) rate of the sediment were measured using an autonomous in situ benthic lander equipped with a benthic chamber (KIOST BelcII) and a microprofiler (KIOST BelpII). The TOU rate was in the range of 1.51 to 1.93 mmol O2 m−2 d−1, about double the DOU rate. The high TOU/DOU ratio implies that the benthic biological activity in the upper sediment layer is one of the important factors controlling benthic remineralization. The in situ oxygen exposure time was about 20 days, which is comparable to the values of other continental margin sediments. The sedimentary Corg oxidation rates ranged from 6.4 to 6.5 g C m−2 yr−1, which accounted for ~2% of the primary production in UB. The Corg burial fluxes ranged from 3.14 ± 0.12 to 3.48 ± 0.60 g C m−2 yr−1, corresponding to more than 30% of the deposited Corg buried into the inactive sediment deep layer. [ABSTRACT FROM AUTHOR]

Integrating seismic interpretation facilitates the discernment of tectonostratigraphic evolution in the eastern Korean continental margin, East Sea. The sedimentary succession of this margin is divided into three major seismic units based on distinct unconformities. These unconformities and their associated seismic characteristics indicate that the eastern Korean continental margin has experienced four evolutionary stages through extensional and subsequent two‐phase tectonic inversions. Early Miocene back‐arc opening of the East Sea triggered the extension of NNW–SSE and N–S trending rifts, resulting in non‐marine to deep‐marine deposition of typical rift‐related linked sedimentological systems in the eastern Korean continental margin. In the early Late Miocene, changes in plate motion and the subduction mode of the Japanese island (NW–SE compression) caused the positive inversion of extensional fault‐bounded half‐grabens in the eastern Korean continental margin, and the Hupo Basin was likely created by the regional flexural response. During this depositional period, hemipelagic sedimentation accompanied by episodic gravity‐controlled slope failures was predominant in the deep‐water environment. The subsidence of the Hupo Basin was enhanced by crustal shortening (E–W compression) that was induced by subduction initiation at the western margin of the Ulleung Basin during the late Early Pliocene (ca. 3.8 Ma). At that time, sedimentary environment gradually became shallower with time and coarse‐grained terrigenous input into the Hupo Basin began so that shallow‐ to deep‐marine sedimentation occurred. In the Quaternary period, the uplift of the Hupo Bank and coeval subsidence of the Hupo Basin were maintained by continued compressive neotectonics. The shallow‐ to deep‐marine deposition continued, but greater quantities of coarse‐grained terrestrial sediment were transported into the Hupo Basin due to combined effects on tectonics and eustasy. Based on the tectonostratigraphic reconstruction developed in this study, we propose that the Hupo Basin is likely a Late Miocene–Quaternary compression‐related basin induced by crustal or thrust loading. [ABSTRACT FROM AUTHOR]

The effects of benthic dissolved organic carbon (DOC) flux on the dynamics of DOC in the deep continental margins (200 – 2000 m depth) is poorly understood. We investigated heterotrophic prokaryotes (hereafter bacteria) production (BP) and the bio-reactive properties of sediment-derived dissolved organic matter (SDOM) to elucidate microbially mediated cause-effect relationships regarding the rapid consumption of dissolved oxygen (DO) and accumulation of humic-like fluorescent DOM (FDOMH) in the deep-water column (750 – 2000 m depth range) of the Ulleung Basin (UB) in the East Sea. BP in the deep water (2.2 μmol C m-3 d-1) of the UB was among the highest reported for various deep-sea sites. The high DOC concentration (55 μM) likely supported the high BP seen in the deep-water column of the UB. Concentrations of DOC and C1 component of the FDOMH, which is indicative of microbial metabolic by-products, were 13-fold and 20-fold greater, respectively, in pore water than in the overlying bottom water, indicating that the sediment in the continental margins is a significant source of DOM in the overlying water column. Fine-scale water sampling revealed that BP near the sediment (0 – 30 m above the seafloor; 2.78 μmol C m-3 d-1) was 1.67 times higher than that measured in the water column above (30 – 100 m above the seafloor; 1.67 μmol C m-3 d-1). In addition, BP increased in the bottom water incubation amended with SDOM-containing pore water (PW). The results demonstrated that SDOM contains bio-reactive forms of DOM that stimulate heterotrophic microbial metabolism at the expense of oxygen in the bottom water layer. The accumulation of C1 component in both PW-amended and unamended bottom water incubation (i.e., without an extra DOM supply from sediment) further indicated that refractory DOM is produced autochthonously in the water column via heterotrophic metabolic activity. This explains in part the microbially mediated accumulation of excess FDOMH in the deep-water column of the UB. Overall results suggest that the benthic release of bio-reactive DOM may be of widespread significance in controlling microbial processes in the deep-water layer of marginal seas.

To identify the sources of organic matter, we examined nitrogen isotopes of the amino acids of sinking particles collected from July 2017 to March 2018 at 1000 and 2250 m in the Ulleung Basin, the southwestern part of the East Sea (Japan Sea). Compared to the 1000 m samples, sinking particles at 2250 m were found to contain more resuspended sediment and underwent more microbial degradation. The signature of microbial degradation was significant in winter-early spring than in late summer-autumn. The source amino acids of sinking particles showed a substantial decline in the isotopic ratio during winter at both depths, suggesting changes in the nitrogen source for primary production. The average trophic positions (TPs) of sinking particles were larger at 1000 m (2.3 ± 0.3) than at 2250 m (1.9 ± 0.2), indicating that organic matter was mainly derived from fecal pellet and other organic debris from heterotrophs. In winter, the average TPs of sinking particles at 1000 m decreased below 2.0, which probably reflects the minimum zooplankton grazing in the euphotic layer. Sinking particles near the seafloor (2250 m) showed lower TP values than those at 1000 m, demonstrating that sinking particles at 2250 m are affected by lateral transport, particularly during winter. Our results show that the nitrogen isotope ratios of amino acids in sinking particles reflect the seasonal dynamics of both nitrogen sources and trophic structure in the water column.

Together with the development of measurement techniques, radiocarbon (14C) has been increasingly used as a key tool to investigate carbon cycling and associated biogeochemistry in the ocean. In this paper, the current status of radiocarbon studies in the East Sea (Japan Sea) is reviewed. Previously, spatiotemporal distribution and change of the water masses in the East Sea from 1979 to 1999 were investigated by using the 14C in the dissolved inorganic carbon (DIC). Researches on sinking particulate organic carbon (POC) revealed that POC in the deep ocean has more complex and heterogeneous origins than we expected. In particular, since 2011, Korean researchers have been collecting sinking particle samples for more than 10 years, so it is expected that 14C of POC will provide important information to understand carbon cycling in relation to climate change. Although the quantity of 14C data published in the East Sea is still limited, the importance and the future direction of using 14C to understand the biogeochemical mechanisms of carbon cycling and its role as a carbon reservoir in the East Sea are detailed herein. [ABSTRACT FROM AUTHOR]

The Ulleung Basin of the East Sea is a biological hotspot, but studies on the macrobenthos therein are lacking. To evaluate the macrobenthos species diversity and community structure in the Ulleung Basin, we conducted a survey from 2017 to 2021. A total of 262 species of macrobenthos was detected by the survey, and the average habitat density was 243 individuals/m2. The average biomass of macrobenthos was 43.7 g/m2, and the average Shannon and Wiener’s diversity index was 2.3 (0.69–3.61). The dominant species were the polychaetes Terebellides horikoshii, Chaetozone setosa, Scalibregma inflatum, and Aglaophamus sp. and the bivalvia Axinopsida subquadrata. The community structure of macrobenthos differed according to water depth, and a correlation analysis using environmental variables showed that the community was affected by water temperature, salinity, and dissolved oxygen. The macrobenthic fauna in the Ulleung Basin was greatly influenced by water depth, the sedimentary environment was different, and the dominant species were also different. In addition, there was little seasonal change compared to the East Sea coast. Our findings will facilitate further investigation of benthic ecosystems throughout the East Sea.

One specimen (38.3 mm SL) of Neoclinus lacunicola Fukao, 1980, belonging to the family Chaenopsidae, was first recorded from Ulleung Island, Korea (East Sea, otherwise known as the Sea of Japan) on 5 January 2021. This species was characterized by paired external pores of incomplete lateral line running from the upper margin of the opercle, seven pairs of supraorbital cirri arranged in two rows, occipital region with a pair of cirri, and 13 rays of pectoral fin. This species is morphologically similar to the Neoclinus toshimaensis Fukao, 1980, but differs in the number of cirri on the supraorbital (6--7 versus 9--11 cirri). This study documents the first report of N. lacunicola in Korean waters and proposes the new Korean name of 'eol-lug-bi-neul-be-do-la-chi' for the species. For the confirmation of the identity of the species, a partial gene sequence of the mt COI (570 bp) of N. lacunicola was obtained for the first time. [ABSTRACT FROM AUTHOR]