East Sea Research Articles

Culicoides dokdoensis, sp. nov. (Diptera: Ceratopogonidae): A new biting midge species from Dokdo Island, Republic of Korea

AbstractRecent molecular approaches toward insect taxonomy are revealing cryptic diversity within biting midge genus Culicoides Latreille, 1809. A new biting midge species was collected from highly restricted area of Dokdo Island, East Sea of the Republic of Korea, and was identified as Culicoides dokdoensis, sp. nov., based on morphological characters and DNA barcoding. The specimens collected from the island were previously known as Culicoides circumscriptus Kieffer, 1918, a cosmopolitan blood‐feeder, due to its morphological similarity. However, the specimens from Dokdo Island can be distinguished from other congeners by the following characters: more curved arms in male aedeagus, wing spot pattern, sensory pit depth, and absence of a spermatheca neck in female. In addition, mitochondrial cytochrome c oxidase I sequence exhibited substantial genetic difference compared to C. circumscriptus populations from the Korean Peninsula, sufficiently supporting the genetic differentiation between the two species. The discovery of this cryptic species highlights the necessity of integrated taxonomy for Culicoides.

Long-Term Trend of Picophytoplankton Contribution to the Phytoplankton Community in the East Sea

Long-Term Trend of Picophytoplankton Contribution to the Phytoplankton Community in the East Sea

Monitoring of Bathymetry Changes in the Coastal Area of Dokdo, East Sea

Monitoring of Bathymetry Changes in the Coastal Area of Dokdo, East Sea

Can the annual bycatch per unit effort of common dolphins (Delphinus delphis) be used to index the species' relative abundance in the East Sea of Korea?

AbstractVisual line‐transect surveys are widely used to estimate the abundance of cetacean populations; however, this method can be prohibitively expensive. Thus, a less expensive alternative method was investigated in the present study, i.e., whether temporal changes in the bycatch per unit effort (BPUE) of cetaceans could be used to index the changes in their abundance. Specifically, the relationship between the annual BPUE of two main bycatch fisheries and the relative abundance of common dolphins (Delphinus delphis) was examined in 2012, 2013, 2015, and 2017 when vessel‐based line‐transect surveys were conducted in the coastal region of the East Sea of Korea. The encounter rate (individuals/km) by study year was significantly correlated with the annual BPUE of set nets. An increase in the density (individuals/km2) of common dolphins, estimated according to a hazard‐rate key function by study year, was associated with an increase in the BPUE of set nets. These results suggest that the annual BPUE of common dolphins could be used to index the species' relative abundance. The BPUE of set nets, which are fixed in coastal regions, reflect the densities of common dolphins in the coastal regions better than that of gill nets used in coastal and offshore regions.

Sources and behaviors of particulate organic carbon, iron, and manganese in the bottom nepheloid layer of the southwestern East Sea (Japan Sea)

The sources and behaviors of particulate organic carbon (POC) and particulate iron and manganese (pFe and pMn, respectively) in the bottom nepheloid layer (or benthic nepheloid layer, BNL) of the southwestern East Sea, also known as the Japan Sea, along a transect from the shelf to the central Ulleung Basin were investigated. The fluxes of POC, pFe, and pMn from the BNL to the seafloor on the shelf and in the basin were determined based on thorium-234 (234Th). The influence of resuspended sediment on POC was quantified using radiocarbon isotope ratio of POC (Δ14C). Sources and behaviors of pFe and pMn in the BNL were investigated by comparison to those of particulate aluminum (pAl). The stable carbon isotope ratios mainly indicated the marine origin of the POC, and the Δ14C values indicated that the majority of the POC in the BNL (68% ± 22%) was supplied by sediment resuspension. pAl and pFe were lithogenic in origin, whereas pMn was mainly authigenic (89–100%). The deficiency of 234Th activity relative to that of 238U increased toward the seafloor in the BNL, implying the efficient removal of 234Th by adsorption to the resuspended sediment particles. The 234Th-based settling fluxes of POC, pAl, pFe, and excess Mn (pMnxs) to the seafloor in the central basin agreed with the results previously obtained from a sediment trap study in the Ulleung Basin. The settling flux of pAl and pFe in the central basin was 2–8% of the lateral transport from the Korea Strait, implying that the transported lithogenic particles mostly settled on the slope before reaching the central basin. In contrast, the settling flux of pMn in the central basin was much larger than that of pMn in the shelf, implying that pMn is further transported toward the central basin or supplied from the local sediments.

A study on the prediction model of water column sound absorption coefficients considering the characteristics of the East Sea of South Korea

East Sea of Korea has the deepest water depth among Korean seas, and the water column changes are distinct in space and time, resulting in a wide range of water column sound absorption coefficients. In this study, we calculate and analysis the spatiotemporal variation of water column sound absorption coefficient in the East Sea of Korea, which has unique oceanographic characteristics. Using extensive CTD data from the Korea Oceanographic Data Centre (KODC) from 1991 to 2021, we calculate the sound absorption coefficient using the widely applied Francois–Garrison model and reveal the unique absorption characteristics of the East Sea. The derived coefficients are then used to calibrate and improve past multibeam echosounder system (MBES) data, which suffered from incomplete water column information and arbitrary mean values. To facilitate the calculation and development of sound absorption coefficient, a MATLAB-based graphical user interface (GUI) was developed. The results of this study contribute to the calculation and inference of sound absorption coefficients along spatial and temporal dimensions of the water column in the East Sea and to the extraction of more accurate seafloor information from MBES data. This study developed the way for future research focusing on algorithmic advances and new methodologies for the calculation of sound absorption coefficients in the West and South Seas of Korea.

A newly recorded brittle star, <i>Amphiophiura megapoma</i> (Ophiuroidea: Ophiurida: Ophiopyrgidae), from the mesophotic zone in the East Sea, Korea

A newly recorded brittle star, <i>Amphiophiura megapoma</i> (Ophiuroidea: Ophiurida: Ophiopyrgidae), from the mesophotic zone in the East Sea, Korea

WAVE ANALYSIS FOR THE DEVELOPMENT OF THIEN NGA - HAI AU OIL FIELD

This study utilizes the SWAN model to simulate wave data, subsequently comparing it with ERA5 and CMEMS wave reanalysis datasets. Our analysis demonstrates that the SWAN-simulated wave data are more consistent with observations compared to ERA5 and CMEMS reanalyzed wave data. The predominant wave directions are Northeast and Southwest, with occurrence frequencies of 43.87% and 24.24%, and maximum significant wave heights of 7.72 m and 3.28 m, respectively. Significant wave heights for 50 and 100 year return periods are 8.17 m and 8.53 m in the NE direction, 3.44 m and 3.56 m in the SW direction, 3.78 m and 3.84 m during the Southwest monsoon, 10.09 m and 10.45 m during the Northeast monsoon, and 12.8 m and 13.6 m during storms, respectively. These results are instrumental for the structural design of the Thien Nga - Hai Au oil field in the Southern region of the East Sea Viet Nam.

Light Intensity Required for the Spring Phytoplankton Bloom in the East Sea

Light Intensity Required for the Spring Phytoplankton Bloom in the East Sea

The Impact of Changes in Sea Level and East Asian Monsoon on Sediment Transport on the Sunda Shelf Since the Last Deglaciation

AbstractThe Sunda Shelf plays a key role in the sedimentation of the southern South China Sea (SCS). However, the impact of past climate changes on sediment transfer to the Sunda Shelf and the southern SCS is still unresolved. Here, we present new data on grain size, clay mineralogy, and Sr‐Nd isotopes of three marine cores, river sediments, and surface sediments of the Sunda Shelf. The results indicate that clay fractions of the central Sunda Shelf and the Gulf of Thailand derived mainly from the Mekong River and the rivers of northern Thailand since the last deglaciation. Significant changes in sediment sources are observed at 7.5 cal ka BP. From 13.3 to 7.5 cal ka BP, sediments in the Gulf of Thailand mainly originated from the rivers of northern Thailand, with contributions from the Mekong River increasing after 7.5 cal ka BP. An opposite shift is observed in the central Sunda Shelf. Such variations in the spatial distribution result from a combination of sea level and East Asian monsoon effects. After 7.5 cal ka BP, less Mekong River sediments were transported southeastwards into the southern SCS, and more sediments were gradually trapped within the delta and transported in a southwesterly direction into the Gulf of Thailand due to intense East Asian winter monsoon, which forced a strong southwestward coastal current. Our results demonstrate the important impact of East Asian winter monsoon strengthening and sea level rise in the mid‐Holocene, which can change sediment sources and transport processes on the Sunda Shelf.

Role of inherited fault reactivation in accommodating multistage deformation in the southwestern margin of the Ulleung Basin, East Sea (Sea of Japan): Insights from 3D seismic interpretation

The southwestern margin of the Ulleung Basin, the East Sea (Sea of Japan), preserves complex structural and stratigraphic architectures produced by a multistage tectonic evolution in response to the Cenozoic convergence of the Indian and Pacific/Philippine Sea Plates to the Eurasian Plate. However, the origin, geometry, kinematics, and interrelationship of geological structures that evolved through the multistage tectonic deformation remain elusive, particularly regarding the role of structural inheritance in the evolution of the basin. Based on comprehensive 2D and 3D multichannel seismic reflection and well data, we present structural interpretations of regional-scale faults, folds, and growth strata in the southwestern margin of the Ulleung Basin, with a focus on inherited fault reactivation. In addition, a revisited deformation framework is proposed, involving back-arc extension/normal faulting (stage 1: ca. 23 to 15 Ma), positive inversion/reverse faulting (stage 2: 15 to 10.6 Ma), and strike-slip faulting/local transpression (stage 3: 10.6 Ma to present). Here, we illustrate how the reverse reactivation and propagation of segmented NE–SW normal faults and subsequent strike-slip movement have led to the complex structural and stratigraphic architectures presently evident in the study area. Notably, the final overprinting of a strike-slip deformation on the inherited NE–SW faults during deformation stage 3 has caused significantly damaged stepovers and tips, in which secondary faults and folds might control hydrocarbon migration/trapping and leakage. In this context, we suggest that the gentle antiformal Gorae Ⅰ structure is linked in origin to the Gorae Ⅴ structure, bearing a commercially viable gas trap as a detachment fold system formed by local transpression during deformation stage 3. Our comprehensive 3D structural seismic interpretation increases the understanding of Cenozoic multistage deformation, highlighting the impact of different tectonic drivers affecting the eastern marginal sea of the Eurasian Plate.

Metagenomic data from surface seawater of the east coast of South Korea

The East Sea, also known as the Sea of Japan, is a marginal sea located in the western Pacific Ocean, displaying comparable characteristics to Earth’s oceans, thereby meriting its recognition as a “miniature ocean”. The East Sea exhibits a range of annually-recurring biogeochemical features in accordance with seasonal fluctuations, such as phytoplankton blooms during the spring and autumn seasons. Despite ongoing monitoring efforts focused on water quality and physicochemical parameters, the investigation of prokaryotic assemblages in the East Sea, encompassing seasonal variations, has been infrequently pursued. Here, we present a monthly time-series metagenomic dataset spanning a one-year period in 2009, obtained from surface (10 m) seawater samples collected off the coast of the East Sea. The dataset encompasses 12 metagenomes, amounting 195 Gbp, with 14.73–22.52 Gbp per sample. This dataset is accompanied by concurrently measured physicochemical parameters. Our anticipation is that these metagenomes will facilitate extensive investigations aimed at elucidating various aspects of the marine microbial ecosystems in the East Sea.

The first high-quality genome assembly and annotation of Patiria pectinifera

The blue bat star, a highly adaptive species in the East Sea of Korea, has displayed remarkable success in adapting to recent climate change. The genetic mechanisms behind this success were not well-understood, prompting our report on the first chromosome-level assembly of the Patiria genus. We assembled the genome using Nanopore and Illumina sequences, yielding a total length of 615 Mb and a scaffold N50 of 24,204,423 bp. Hi-C analysis allowed us to anchor the scaffold sequences onto 22 pseudochromosomes. K-mer based analysis revealed 5.16% heterozygosity rate of the genome, higher than any previously reported echinoderm species. Our transposable element analysis exposed a substantial number of genome-wide retrotransposons and DNA transposons. These results offer valuable resources for understanding the evolutionary mechanisms behind P. pectinifera’s successful adaptation in fluctuating environments.

Monitoring of 137Cs, 239+240Pu, and 90Sr in the marine environment of South Korea and their impact on marine biota: 10 years after the Fukushima accident

This study conducted an analysis of the behavior of radionuclides and assessment their radioactive risk based on seawater and seabed sediment samples gathered from the East, South, and Yellow Seas of South Korea over the period from 2011 to 2020. The distribution for each radionuclides in seawater obtained from the East, South, and Yellow Seas were similar. However, the concentrations of 137Cs and 239+240Pu in sediments from the East Sea were observed to be higher compared to those from the South and Yellow Seas. This variation can be attributed to differences in the ocean inflow, water column properties, and seabed characteristics among the seas around South Korea. There were no statistically significant differences between the radioactive concentrations of seawater and seabed samples collected before and after the Fukushima accident, and no areas with unusually high radiation levels were detected. Using the distribution coefficient (Kds) and the concentration ratio (CR) calculated from the 2011-to-2020 data, we evaluated the radiological impact on fish. The ERICA tool was utilized to assess these data, and indicated a negligible radiological risk from radioactivity in the seawater, seabed sediments, and marine biota in the South Korean Ocean.

First Millennium Urbanism in Central Asia: Typology and Evolution of Dzhety-asar Settlements

Abstract Despite its apparent size and length of its existence, the Dzhety-asar culture of Kazakhstan remains one of the great unknowns of Central Asian archaeology, comprising, as it did, several dozen now-ruined settlements with an almost thousand-year long occupational history. First settled around the 1st century BC and gradually abandoned in the second half of the 1st millennium AD, the Dzhety-asar towns and manors were located to the east of the Aral Sea within the Syr Darya delta, and may have functioned as a core element in Central Asia’s medieval trade networks. Despite past research efforts by the Khorezmian Archaeological Ethnographic Expedition (KhAEE), the cultural and political history of the Dzhety-asar people remains largely unclear, with as yet no consensus on the political structure or their ethnic, linguistic and religious make-up. The present paper does not presume to answer these questions at this stage, as it is the result of two fieldwork seasons documenting and surveying Dzhety-asar settlements. It is, instead, intended to lay out the preliminary findings, presenting a revised typology of sites, and suggest initial hypotheses regarding the structure and possible evolution of the culture.

Assessing the Ensemble Assimilation System for Forecasting the Genesis of Tropical Cyclone Sonca (2017) in the Vietnam East Sea using a Lagrangian Approach

: With the aim of evaluating the cyclogenesis predictability of Sonca (2017) using an ensemble prediction system from the local ensemble transform Kalman filter (LETKF) to model WRF, the study proposed a dynamical assessment method with a Lagrangian approach that is stable and independent of time and reference systes. With this approach, the study can clearly distinguish between cases of tropical cyclone (TC) formation and non-formation in the ensemble forecast members. By evaluating the thermodynamic conditions of the low-level circulation between the forming and non-forming groups, the study found that the ocean-atmosphere interaction and the vortex merger process play imnportant roles in the formation of Sonca. The evaluation of the formation location showed that the detected vortex centers from the forming members tended to concentrate near the monsoon trough axis, indicating that this is a highly favorable region for vortex formation in the Vietnam East Sea.
 
 

Developmental history of a newly discovered chain of paired mound and depression structures on the southwestern continental shelf of the Ulleung Basin, East Sea, Korea

A chain of paired mound and depression structures are presented in the southwestern continental shelf of the Ulleung Basin, East Sea, Korea. We integrate multibeam bathymetry to identify topographic features, sub-bottom profile and multi-channel seismic reflection data to confirm geological features, and piston cores to understand the sediments of the mounds and depressions. Paired structures occur with a northwest–southeast orientation at water depths between 130 and 150 m and have similar scales of 10–20 m in height and depth. The mounds consist of cold-water corals and authigenic carbonate with shelly sand, whereas, the surficial lithology of depressions are only composed of siliciclastic deposits. The mounds appeared to have grown from the depression based on the observation for morphological features in the cross-section profiles of the paired mound and depression structures. Seismic profiles show acoustic blanking anomalies and seismic chimneys, indicating that the topographic relief formed under the influence of gas seepage. The petrological and geochemical signature of carbonate chunks also displayed gas leak effects different from CWC. This study suggests a developmental history model with paired mound and depression structures, in which gas/fluid escape causes depressions and the selective coral growth creates mounds growing on one side of these depressions. The mounds had sufficiently grown, depressions would have been further developed in interaction with the bottom current.

Delineation of shallow volcanic structures from audio-frequency magnetotelluric data beneath Ulleung Island, East Sea (Sea of Japan)

As volcanoes are closely related to the living environment of humans, in particular via natural hazards and geothermal energy, scientific studies on volcanic edifice structures are required. Ulleung Island is a Quaternary volcanic island located in the mid-western East Sea (Sea of Japan). In this study, we conducted an audio-frequency magnetotelluric (AMT) survey to image the substructure of the Ulleung volcanic edifice. In addition, the electrical structure was interpreted from the geothermal system perspective, geochemical compositions of volcanic rocks, and the possibility of the presence of a magma reservoir. AMT data were obtained from 25 stations and processed using the remote reference technique. Then, the three-dimensional (3-D) approach was reasonably adopted according to dimensionality analysis. Before conducting the 3-D inversion, the effects on topography and ocean were analyzed using a simplified 3-D synthetic model, because Ulleung Island is surrounded by sea and the topography is undulating. Most AMT stations on Ulleung Island are distorted by topographical and oceanic effects; in particular, oceanic effects are significant at frequencies lower than 10 Hz. The 3-D inversion was conducted with full impedance components and vertical magnetic transfer functions in a frequency range of 10,000–1 Hz. The results show that the Ulleung volcanic edifice is characterized by two layers of electrical structures as follows: near-surface resistive anomalies and an underlying conductive layer. Considering the high geothermal gradient on Ulleung Island, we suggest that the conductive layer of the volcanic edifice is due to hydrothermal alteration of basaltic rocks, with a potential heat source underneath. Based on the geochemical characteristics of the Ulleung volcanic rocks, the possibility of heat transfer from a trachytic magma reservoir within the shallow crustal is suggested. In summary, this study presents a geological interpretation of shallow volcanic structures beneath Ulleung Island and the possibility of an active magma reservoir as a potential heat source for the volcanic edifice.Graphical

AN APPLICATION OF 1-D MODEL FOR ASSESSING SALINE INTRUSION IN THE COASTAL AREAS OF THE VIETNAMESE MEKONG DELTA

Many studies in present years have been conducted to predict the effects of changes in the upstream discharge, hydrodynamics, and saline intrusion in the coastal of the Vietnamese Mekong Delta (VMD) (Smajgl et al., 2015; T. Van et al., 2013); however, the models for the entire delta did not show detail for small areas such as the Ca Mau Peninsula, and other studies were only considered in upstream flooding condition such as the Long Xuyen Quadrangle (Nguyen et al., 2012; T. Van et al., 2013). Besides, several study were using hydraulic models for the whole VMD region; Nevertheless, these studies were only interested in major river systems that applied the Mike 11 salt simulation model for the VMD region. Some hydraulic studies were simulated in specific region such as Long Xuyen Quadrangle. However, a few studies have focused on a complex river system such as Quan Lo Phung Hiep (QLPH) area of the Ca Mau peninsula, which is characterized by a complex river system, inter-regional irrigation works, and a variety of water demands, including marine, brackish, and freshwater-based agriculture. However, coastal studies, particularly those of an inter-regional character with complicated river networks like the QLPH, have received little attention. As a result, this research was carried out to assess the hydrodynamics and saline intrusions of the interwoven river network's coastal area, a complex operating system in a large area affected by both tidal regimes in the West and East Sea, which is characteristic of the Mekong Delta.

Maritime security or economic growth: The choice of stakeholders in coastal tourism development in Binh Dai district, Ben Tre province, Vietnam

Coastal tourism emerges as a diverse, dynamic, fast-growing, and economically attractive form of contemporary tourism that encompasses a range of tourism, leisure- and recreational-oriented facilities and activities. As the coastline resembles a composite of ecological, social cultural, and economic values, it is of considerable interest to people, processes, and industries. Vietnam possesses the strategic advantage of a vast coastline spanning the entire length of the country, coupled with its location within the language zone of the East Sea, a crucial trading route for global commerce. Alongside the exploitation of marine resources, oil and gas, transportation, and port services, the development of coastal tourism is deemed a critical sector in promoting the growth of the maritime economy. Nevertheless, due to the national strategic position, the development of tourism in coastal areas faces challenges in reconciling national security policies for coastal defense with the goal of promoting economic development. This article examines the implementation of maritime economic development policies in Binh Dai district, Ben Tre province, highlighting a strategic balance between maintaining maritime security and promoting economic development for stakeholders. The study reveals that sustainable development in coastal tourism is not solely concerned with the livelihoods of local communities and environmental protection, which are typical concerns in other forms of tourism, rather, in the context of Binh Dai district, Ben Tre province, it is also tightly linked to maritime security.