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We examined the architecture of Pleistocene sequences of the Korea Strait (KS) margin controlled by ocean currents and compressional tectonic regimes, using a dense grid of high-resolution single-channel seismic profiles and sediment cores. Along with uplifted strata featuring an erosional and/or non-depositional flat seabed in the northern shelf of the study area, three Middle–Upper Pleistocene sequences are characterized by forced regressive deposits recorded at 100-ka intervals covering one postglacial sequence across the shelf. The three forced regressions together comprise an offlapping stacking pattern, where the degree of erosion of the upper surface of the older sequence is greater than that of the younger sequence. The tectonic tilt involved in landward uplift and seaward subsidence across the shelf basin causes differential erosional rates among the forced regression deposits. The Upper Pleistocene forced regression deposits are preserved as a set of 20-ka clinoform wedges with aggradational to progradational stacking patterns, leading to a falling stage systems tract (FSST) during the stepwise fall in sea level, followed by a shelf edge-perched lowstand systems tract (LST) wedge during the Last Glacial Maximum (LGM). The northeast-facing Tsushima Current (TC) passing through the KS played an important role in allowing the fine sediments originating from the Nakdong River to form the FSST clinoform wedges and the LST oblique prograding delta lobe along the shelf break.

Understanding the trophic ecology of the giant Pacific octopus Enteroctopus dofleini is challenging in developing marine ranches and in reestablishing its regional stocks against the severe stress of fishing. We adopted carbon and nitrogen stable isotope techniques (termed δ13C and δ15N, respectively) to identify the trophic niche (i.e., pathways and positions) of this species systematically in the entire food webs of two marine ranches off the east coast of the Korean peninsula. While a slight spatial shift in the isotopic nestedness of faunal communities was observed, the δ13C and δ15N values of consumers were distinct and separate among functional groups at both ranches. The consumer δ13C values spanned a broad range between pelagic and benthic sources of organic matter, and their δ15N values recorded a stepwise trophic-level enrichment, indicating that suspension feeders and herbivore-deposit feeders served as baselines of pelagic- and benthic-based trophic pathways, respectively. The δ13C values of predators, including E. dofleini, were arrayed between the two primary consumer groups. Neither δ13C nor δ15N values showed any remarkable variations with increasing octopus weight. Dietary mixing-model calculations indicated that E. dofleini is a generalist predator relying on both benthic- and pelagic-affinity prey, similar to some teleost species that consume a diverse spectrum of prey. In contrast, other teleost groups showed prevalent trophic links with either pelagic- or benthic-based pathways. The trophic-level estimations revealed that E. dofleini occupies an intermediate position slightly below the teleosts. A lack of discrete trophic positions between E. dofleini and teleosts seemed to be indicative of the released teleost predation but instead reflects the imposed food competition. Overall, the results demonstrated that despite compositional changes in the taxa constituting individual trophic groups, E. dofleini occupied a very similar trophic niche in both ranching systems. Finally, as extracted from information based on octopus marine ranches launched on natural rocky bottoms, our isotopic evidence provides a greater understanding of the trophic ecology of this octopus species in nearshore natural habitats along the southwestern margin of its distribution range.

Choi, D.-L.; Shin, D.-H.; Jin, J.-Y.; Lee. Y.-K., and Kum, B.-C., 2020. High-resolution seismic stratigraphy offshore Haeundae beach in Busan, South Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 187-193. Coconut Creek (Florida), ISSN 0749-0208.The stratigraphic architecture of the Haeundae shallow sea was evaluated using numerous high-resolution single-channel seismic profiles and drilled cores. Two major seismic units over the basement, the lower Unit II and upper Unit I, as well as two subunits (Units Ia and Ib) in the upper Unit I were identified in the study area. Unit II shows numerous chaotic diffraction hyperbolic seismic reflection patterns overlying high amplitude, and irregular reflection of the bedrock surface, corresponding well with the gravel-dominated deposits. Unit II is interpreted as nonmarine alluvial deposits in the Quaternary glaciations. Unit I is present over Unit II with two distinct subunits at different locations: Unit Ia, distributed inshore within ∼10 m depth, and Unit Ib, offshore beyond ∼13 m depth. Unit Ia, which is accumulated more in the western inshore section, exhibits an acoustically semi-transparent and sigmoidal clinoform wedge and is well correlated with sand-dominated deposits from core data. Unit Ib, which pinches out landward but gradually thickens seaward, is generally characterized by transparent seismic facies, likely made up of very fine sandy to muddy sediments from surface sediments. The depositional environments of Units Ia and Ib are categorized as shoreface settings and the landward innermost part of the Nakdong distal delta system during late Holocene sea-level highstand, respectively. Due to severe weather conditions associated with winter storms and summer typhoons as well as human interventions, the sediment morphology and its distribution are thought to have constantly been reactivated and modified.

High-resolution multichannel seismic data were collected to identify depositional sequences on the southwestern shelf of the Ulleung Basin, where a unidirectional ocean current is dominant at water depths exceeding 130 m. Four aggradational stratigraphic sequences with a 100,000-year cycle were recognized since marine isotope stage (MIS) 10. These sequences consist only of lowstand systems tracts (LSTs) and falling-stage systems tracts (FSSTs). Prograding wedge-shaped deposits are present in the LSTs near the shelf break. Oblique progradational clinoforms of forced regressive deposits are present in the FSSTs on the outer continental shelf. Each FSST has non-uniform forced regressional stratal geometries, reflecting that the origins of sediments in each depositional sequence changed when sea level was falling. Slump deposits are characteristically developed in the upper layer of the FSSTs, and this was used as evidence to distinguish the sequence boundaries. The subsidence rates around the shelf break reached as much as 0.6 mm/year since MIS 10, which contributed to the well-preserved depositional sequence. During the Quaternary sea-level change, the water depth in the Korea Strait declined and the intensity of the Tsushima Current flowing near the bottom of the inner continental shelf increased. This resulted in greater erosion of sediments that were delivered to the outer continental shelf, which was the main cause of sediment deposition on the deep, low-angled outer shelf. Therefore, a depositional sequence formation model that consists of only FSSTs and LSTs, excluding highstand systems tracts (HSTs) and transgressive systems tracts (TSTs), best explains the depositional sequence beneath this shelf margin dominated by a geostrophic current.

The molecular composition and distribution of sterols were investigated in the East China Sea to identify the origins of suspended particulate matter (SPM) in offshore waters influenced by Changjiang River Diluted Water (CRDW). Total sterol concentrations ranged from 3200 to 31,900pgL(-1) and 663 to 5690pgL(-1) in the particulate and dissolved phases, respectively. Marine sterols dominated representing 71% and 66% in the particulate and dissolved phases, respectively. Typical sewage markers, such as coprostanol, were usually absent at ~250km offshore. However, sterols from allochthonous terrestrial plants were still detected at these sites. A negative relationship was observed between salinity and concentrations of terrestrial sterols in SPM, suggesting that significant amounts of terrestrial particulate matter traveled long distance offshore in the East China Sea, and the Changjiang River Diluted Water (CRDW) was an effective carrier of land-derived particulate organic matter to the offshore East China Sea.

A sequence stratigraphic analysis was conducted using high-resolution ‘Chirp’ seismic profiles and a long core data off the Nakdong River where Holocene deltaic deposition prevails in the Korea Strait. The depositional sequence comprises a group of transgressive and highstand systems tracts, intercalated with their bounding surfaces of maximum flooding surfaces, above a sequence boundary. It is formed by an erosional process within an incised valley, indicating the Nakdong River at the lowstand of sea level. The transgressive systems tract consists of the lower and upper depositional units, bounded by a ravinement surface, formed during the early Holocene when sea-level rose between 12.0 and 6.0 ka BP. The lower depositional unit mostly occurs in the incised valley area, comprising fluvio-estuarine sediments, whereas the upper one nearshore environments consist of sand sheet and ridges. The overall stacking pattern of these sequences demonstrates retrogradation. During the late Holocene sea-level highstand of around 6.0 ka BP, the highstand systems tract overlying the maximum flooding surface consists of the deltaic sequence, formed as a seaward sigmoid progradational pattern. The subaqueous Nakdong delta system has evolved to depositional units of the retrogradational transgressive and then the progradational highstand systems tract over a sequence boundary during the Holocene transgression.

The South Korea Plateau is a remnant of continental crust in the middle of the eastern Korean margin that was deformed by extension in association with back-arc rifting and separation of the southwestern Japan Arc in the Cenozoic. Multichannel seismic profiles show that the South Korea Plateau preserves structure of rift basins flanked by uplifted footwall blocks. Rift basins in the plateau are filled with distinct syn- and post-rift sequences separated by a prominent breakup unconformity resulting from uplift. The crustal and upper mantle structures computed by ambient noise tomography indicate that the South Korea Plateau defines the seaward limit of rifted continental crust; in addition, rifting occurred with vigorous asthenospheric upwelling induced along the Korean margin and depth-dependent stretching. Therefore, the South Korea Plateau underwent the entire sequence of tectonic events typical of a passive continental margin encompassing rifting with subsidence, uplift, erosion, and breakup prior to the separation of the southwestern Japan Arc. Breakup at the Korean margin may substantiate successive episodes of back-arc spreading which migrated toward the arc in response to trench retreat. We suggest that the southwestern Japan Arc moved to its present location from the southern part of the Korean margin with a significant amount of clockwise rotation during back-arc spreading.

High-resolution seismic profiles coupled with sediment sampling were analyzed to investigate the acoustic characters and distribution patterns of the late Holocene sediments in Gamak Bay of the South Sea, Korea. The mean grain size of surficial sediment lies around . Sediments in the bay consist of silt and clay with progressive decrease toward the inner bay. The seismic sedimentary sequence overlying the acoustic basement can be divided into two sedimentary units (GB I and II) by a prominent mid-reflector (Maximum Flooding Surface; MFS). The acoustic basement occurs at the depth between 20 m and 40 m below the sea-level and deepens gradually southward. The GB I, mostly occupying the channel-fill, is characterized by reflection-free seismic facies. It can be formed as late Transgressive System Tract (TST), interpreted tidal environment deposits. MFS appears at the depth of about 15~28 m below the sea-level and is well defined by even and continuous reflectors on the seismic profile. The GB II overlying MFS is composed of acoustically transparent to semitransparent and parallel internal reflectors. GB II is interpreted as the Highstand System Tract (HST) probably deposited during the last 6,000 yrs when the sea level was close to the present level. Especially, it is though that the GB II was subdivided into two layers (GB II-a and II-b) by a HST-reflector and this was classified by wind, sea water flux, and tidal current.

Multi-channel seismic profiles and swath bathymetric data were used to investigate the tectonic evolution of the South Korea Plateau (SKP) associated with the opening of the East Sea (Japan Sea). The SKP is a deformed fragment of continental crust with numerous horsts and sediment-filled grabens. Three sedimentary units in the plateau were identified, which consist of the lower sequence (Unit I) interpreted as syn-rifting deposition during the early to middle Miocene, and the middle and upper sequences (Units II and III) considered as post-rifting deposition since the late Miocene. The fault system in the SKP includes the South Korea Plateau Fault (SKPF) trending NNW-SSE and smaller en echelon normal faults oriented NE-SW. We interpreted the information to postulate that the formation of the SKPF is the result of divergent right-lateral strike-slip movement in the SKP. This study suggests that the dextral movement of the SKP was induced by WSW-ward propagation of the spreading center located in the Japan Basin from the early to middle Miocene times.

We investigated the biogeochemical constituents, microbial communities and functional genes (mcr and dsr) associated with anaerobic methane oxidation and sulfate reduction, and metabolic activities by sulfate reduction in the sulfate–methane transition zone (SMTZ) of gas-hydrate-bearing sediment of the Ulleung Basin in the East Sea. Maxima in the sulfate reduction rate (12.6 nmol cm−3 d−1), CO concentration (83 μM), and gene abundances of dsrA (9.1 × 106 copies cm−3) and mcrA (11.6 × 106 copies cm−3) occurred in the SMTZ. The peaks of CO consistently found in the SMTZ suggested that CO is an intermediate metabolic product related to methane oxidation. Candidate division JS1, the predominant bacterial group that comprised 59.0–63.7% of the 16S rRNA gene sequences, was recognized as an important organic carbon oxidizer. Both Marine Benthic Group D (MBGD) and Marine Benthic Group B (MBGB), which constituted 40.8–52.9 and 10.3–43.9% of the 16S rRNA gene sequences, respectively, were the dominant archaeal groups. Analysis of functional gene diversity revealed that anaerobic methanotroph-1-related phylotypes appeared to be the major CH4 oxidizer, whereas Firmicutes-like group was a predominant sulfate reducer in the 0.8 mbsf in SMTZ with low SO42− concentration. Overall results indicated that JS1 and two archaeal groups (MBGB and MBGD) seem to play a significant role in carbon and elements cycles in the gas-hydrate-bearing subsurface sediment of the Ulleung Basin.

The eggs of the Pacific oyster, Crassostraea gigas, become infertile when infected by the parasite Marteilioides chungmuensis. Histologically, M. chungmuensis infects the oyster oocyte cytoplasm, and the ovaries take on a "lumpy" appearance once infected, which lowers commercial value of the oyster. This has a negative economic impact on oyster farms in South Korea and Japan. In this study, we compared traditional diagnostic methods (histology) with two molecular-based methods (polymerase chain reaction [PCR] amplification and in situ hybridization [ISH]) to identify M. chungmuensis-infected oysters. The efficacy of PCR and ISH to identify M. chungmuensis-infected oysters was compared to that of routine histology in 100 oysters. Thirty infections were identified using PCR and 16 using histology, whereas 31 infections were identified using ISH. The ISH and PCR assays were more sensitive compared to using histology with standard epidemiological methods. We strongly recommend that early parasitic invasion should be monitored with PCR/ISH methodologies as a basis for developing effective diagnostic techniques to identify M. chungmuensis-infected oysters.

Tintinnid species distribution has been monitored in the northern East China Sea (ECS) in the summer of 2006 through 2011. This is used to understand the water mass movements in the northern ECS. The warm oceanic tintinnid species had largely spread in 2007 in the area, indicating that there was greater warm water extension into the northern ECS. However the extension of neritic water within the Changjiang diluted water mass has strengthened in 2008 and 2010 because the neritic species distribution had relatively grown in both years. These annual results based on the biological indicators of tintinnid species are well matched with the salinity change in the area. The warm oceanic species, Dadayiella ganymedes had frequently occurred over the study years and had shown a significant relationship with the salinity change. This is valuable as a key stone species for monitoring the intrusion of the Kuroshio within the northern ECS. Information from tintinnid biological indicators can support physical oceanography data to confirm ambiguous water mass properties.

An attempt has been made using the molecular signatures of anthropogenic persistent organic chemicals such as DDTs and PCBs and sterol biomarkers in suspended particulate matter (SPM) to verify certain biogeochemical postulations, especially the origin of low salinity water mass and SPM in a river plume ecosystem in the Yellow Sea. This investigation was also assisted by satellite imagery using SeaWiFS and concurrent measurement of salinity. The target chemicals were measured in SPM, sampled near Yangtze River mouth to stations that were close to Jeju Island, Korea. ΣDDTs and ΣPCBs in SPM were at ultra trace levels (parts-per-quadrillion) ranging from 3.3 to 39 and from 20 to 68 pg L −1 , respectively; while Σsterols occurred from 3200 to 32,000 pg L −1 range. The spatial distribution and molecular compositions were studied. This study illustrated the effectiveness of unconventional molecular tracers in identifying water masses and movement of riverine plumes to regional seas in the transport of sediments and contaminants. Additionally, it highlighted the importance of long range-longitudinal transport of contaminants (transboundary pollution) in regional seas and their impact on the ecosystem.

The mortality of the tunicate Halocynthia roretzi due to softness syndrome, which exhibits tunic thinning as well as loss of muscle elasticity, has caused serious problems for the aquaculture industry in Korea. The effects of softness syndrome can be better understood by studying the defense mechanisms of Halocynthia roretzi . This study used flow cytometry to assess hemocyte parameters in H. roretzi . Flow cytometry provided a means to rapidly quantify tunicate defense mechanisms by measuring temperature and zymosan-dependent effects on phagocytosis activity. Also, immune parameters, such as morphology of cell sub-populations (size and granularity), total hemocyte counts (THC), hemocyte viability, and phagocytosis activity using flow cytometry analysis, of normal tunicates and softness syndrome tunicates were compared. The results showed that, in normal tunicates, the phagocytic rate and hemocyte viability are higher than those of tunicates with softness syndrome. Total hemocyte numbers in softness syndrome tunicates were 4 times higher than that of normal tunicates. It is suggested that the tunicate immune system is associated with softness syndrome and that flow cytometry is a powerful tool for characterizing immune response.

In conjunction with geochemical characteristics, rate of sulfate reduction was investigated at two sediment sites in the continental slope and rise (basin) of the Ulleung Basin in the East Sea. Geochemical sediment analysis revealed that the surface sediments of the basin site (D2) were enriched with manganese oxides (348 μ㏖ ㎝?³) and iron oxides (133 μ㏖ ㎝?³), whereas total reduced sulfur (TRS) in the solid phase was nearly depleted. Sulfate reduction rates (SRRs) ranged from 20.96 to 92.87 n㏖ ㎝?³ d?¹ at the slope site (M1) and from 0.65 to 22.32 n㏖ ㎝?³ d?¹ at the basin site (D2). Depth integrated SRR within the top 10 ㎝ depth of the slope site (M1; 5.25 m㏖ m?² d?¹) was approximately 6 times higher than that at the basin site (D2; 0.94 m㏖ m?² d?¹) despite high organic content (＞2.0% dry wt.) in the sediment of both sites. The results indicate that the spatial variations of sulfate reduction are affected by the distribution of manganese oxide and iron oxide-enriched surface sediment of the Ulleung Basin.

Despite its importance in carbon mineralization pathways, relatively little is known about sulfate reduction along a continental slope and rise. We investigated the temporal and spatial variations and controls of sulfate reduction rates (SRRs) in the continental margin sediment of the Ulleung basin (UB), off the southeast Korean upwelling system in the East Sea. SRRs ranged from 1.22 to 8.07 mmol m−2 d−1 at the slope sites and from 0.69 to 3.18 mmol m−2 d−1 at the basin sites. These values were exceptionally higher than those observed within other marginal seas and were comparable to SRR values at the same depth range in the Peruvian and Chilean upwelling systems. The high sulfate reduction in the UB was attributable to enhanced primary production in the water column associated with coastal upwelling and a high export flux of large organic particles into the basin via the Ulleung warm eddy. The depth integrated SRR was approximately 4 times higher in the highly productive spring (4.91 ± 2.55 mmol m−2 d−1)...

Authigenic carbonates were sampled in methane-enriched piston core sediments collected from gas venting sites on the western continental slope of the Ulleung Basin, East Sea of Korea. Multidisciplinary investigations on these carbonates, including the scanning electronic microscope (SEM) observations and mineralogical-geochemical compositions, were carried out to identify the carbon and oxygen sources and the forming mechanism of these carbonates. The authigenic carbonates from the study area correspond to semi-consolidated, compact concretions or nodules ranging from 2 to 9 cm in size. X-ray diffraction and electron microprobe analyses showed that most of the sampled carbonate concretions were composed of almost purely authigenic high-Mg calcite (10.7-14.3 mol% MgCO(3)). Characteristically, microbial structures such as filaments and rods, which were probably associated with the authigenic minerals, were abundantly observed within the carbonate matrix. The carbonates were strongly depleted in delta(13)C (-33.85 parts per thousand to -39.53 parts per thousand Peedee Belemnite (PDB)) and were enriched in delta(18)O (5.16-5.60 parts per thousand PDB), indicating that the primary source of carbon is mainly derived from the anaerobic oxidation of methane. Such methane probably originated from the destabilization of the underlying gas hydrates as strongly supporting from the enriched (18)O levels. Furthermore, the strongly depleted delta(13)C values (-60.7 parts per thousand to -61.6 parts per thousand PDB) of the sediment void gases demonstrate that the majority of the gas venting at the Ulleung Basin is microbial methane by CO(2) reduction. This study provides another example for the formation mechanism of methane-derived authigenic carbonates associated with gas-hydrate decomposition in gas-seeping pockmark environments. (c) 2009 Elsevier Ltd. All rights reserved.

To determine and discriminate the types of tetracycline (Tc)-resistance determinants (tet), we developed a multiplex polymerase chain reaction (PCR). With minimized numbers of primers derived from the variable and conserved regions of six different types of tet genes, tet(A)–(E) and (G), the multiplex PCR was sensitive and specific enough to discriminate the various types of tet genes, even multiple tet genes in an individual resistant isolate, by the different sizes of the resulting PCR products. Each of 20 Tc-resistant Edwardsiella tarda (Ed. tarda) isolates from diseased fish from aquatic farms in Korea carrying either one or two tet genes of types (A), (D), (B), or (G) gave PCR products of the appropriate lengths. Among the four types of tet genes found in Ed. tarda, two types, tet(A) and (D), were always present on mobile plasmids, and the other two types, tet(B) and (G), were located on the nonmobile nucleic acids. This is the first time that either of these two genes, type (B) or (G), have been found in Ed. tarda isolates. The two most common types of Tc-resistance determinant were, tet(A) and (D), occurring in 55% and 45% of total Tc-resistant Ed. tarda isolates, respectively.

We report on a herpes-like virus, which was found to be associated with mass mortality of common carp Cyprinus carpio for the first time in Korea in 1998. The external signs of infection in moribund fish were darkened coloration and severe branchial necrosis in the gill. Transmission electron microscopy revealed the presence of herpes-like viruses in spleen tissue. Infected spleen cells showed hypertrophied nuclei and degeneration. Numerous nucleocapsids of about 82 nm in diameter were found within the nucleus and cytoplasm of infected cells, and extracellular enveloped particles were also observed. We conclude that this virus was a likely significant cause of the high mortality of common carp in Korea in 1998.

During a routine survey of the Pacific oyster Crassostrea gigas in Tongyoung (previously Chungmu) on the southern coast of Korea, basophilic inclusions were observed in the gonadal tissues. They were detected from March to May at a prevalence rate of 3.3 to 7.1%. The inclusion bodies were Feulgen-positive and stained orange-red with phloxine tartrazine. Electron microscopic observation revealed non-enveloped, icosahedral particles 40 to 45 nm in diameter. These morphological characteristics resemble those of papova virus-like inclusions previously described from Pacific and eastern (American) oysters C. virginica in North America. Although many mitochondrial bodies and intact sperm cells were observed around the inclusion body, no host reaction, such as hemocytic infiltration, was detected.

In order to assess changes in the activity of immunecompetency present in Crassostrea gigas infected with Marteilioides chungmuensis (Protozoa), the total hemocyte counts (THC), hemocyte populations, hemocyte viability, and phagocytosis rate were measured in oysters using flow cytometry. THC were increased significantly in oysters infected with M. chungmuensis relative to the healthy appearing oysters (HAO) (P