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Large megathrust ruptures can create notable tsunamis in tectonic back‐arc basins as was documented during the 2011 Tohoku earthquake in the Sea of Japan. We present a physical analysis of the excitation of back‐arc tsunamis by extending the fore‐arc deformation field from the earthquake centroid into the back‐arc basin and identify fault dip as the main geometrical contributor to the propagation of these events. As such, our theoretical model along with a large number of numerical simulations reveal that the dominant period of back‐arc tsunamis is different from that of the fore‐arc waves and thus they are a new class of tsunamis. Through numerical simulations and analysis of data from the 2011 Tohoku event, we show that a combination of near‐ to intermediate‐field horizontal and vertical deformation as well as transient surface waves is necessary to reconstruct the back‐arc propagation. We find that while seismic surface waves can affect coastal tsunami amplitudes in the back‐arc, their effect comes second to that of the horizontal component of deformation as manifested via bathymetric gradient. We then simulate back‐arc tsunamis and the hazard in the Sea of Japan from several potential future earthquake scenarios in the Japan Trench and Nankai Trough. Our results show that the coseismic excitation of back‐arc tsunamis can result in considerable waves close to 1 m in the Sea of Japan, near the Niigata Prefecture from megathrust earthquakes. Plain Language Summary: The 2011 Japan earthquake created a large tsunami in the Pacific Ocean. But it also made a moderate tsunami in the Sea of Japan, on the far side of the Japanese islands. We call these waves Back‐arc tsunamis and study their properties by looking at the contributions of various earthquake aspects including earthquake size, depth, fault geometry, and seismic surface waves, to the generation of these tsunamis. Our work shows that contrary to regular tsunamis, the hazard from back‐arc tsunamis is affected by the fault dip angle (how steep the fault is). We also find that large earthquakes in eastern Japan can create relatively large back‐arc tsunamis (with wave heights exceeding 1 m) in the Sea of Japan. Key Points: We present theoretical and numerical models of back‐arc tsunamis produced by megathrust earthquakesAmong source parameters, seismic moment and fault dip angles determine the dominant period and the spread of back‐arc tsunamisBack‐arc tsunamis from Japan Trench rupture scenarios can reach amplitudes >1 m in the Sea of Japan, and should be included in hazard models [ABSTRACT FROM AUTHOR]

Middle to Late Miocene organic‐rich siliceous mudstones (Onnagawa Formation) in the Akita Basin, Northeast Japan have been an important target for both paleoceanographic studies and hydrocarbon exploration in Japan. However, the reliable age of their formation has remained poorly constrained. Here, we report new zircon U–Pb and fission‐track ages of the Onnagawa Formation from a previously well‐studied outcrop route in the Yashima area, central Akita Basin. The thin tuff bed in the lower Onnagawa Formation was dated at around 11.6 Ma, whereas thin tuff beds in the upper Onnagawa Formation was dated at 10.4–9.6 Ma. The new age model constrains the base of the succession as older than 15.6–13.8 Ma and the top of the succession as 8.7–8.2 Ma. The results suggest that the lowest part of the succession was deposited before the Onnagawa Stage. The new age model indicates a rapid deposition in the lower Onnagawa Stage. The new age model also clarifies a temporary decrease in the sedimentation rate during 10.9–9.4 Ma, which coincided with a hiatus or slow deposition reported from other areas along the Sea of Japan coast. The new age model also revises the timing of paleoceanographic changes, of the best hydrocarbon source horizon, and of hydrothermal activity responsible for seafloor chemoautotrophic communities in the Akita Basin. This revised timing reveals that the onset of paleoceanographic changes from oxidizing to anoxic bottom environments favorable for hydrocarbon source rock formation was closely related to the tectonic uplift of the Northeast Japan Arc at ~12 Ma, whereas the timing of hydrothermal activity was related to the following extensional tectonics at ~9 Ma. The results of this study thus shed light on hitherto unclarified relationships between tectonics, volcanism, and paleoceanographic changes in the Sea of Japan. [ABSTRACT FROM AUTHOR]

Oil spill incidents with tankers, port terminals and offshore platforms impact seriously on marine life and socio-economic services. They occur more and more frequently and require immediate and effective response which starts with good knowledge of the likely pathways of spilled oil in the region where a pollution has occurred. The drift of a hypothetical oil spill from the main oil port in Peter the Great Bay (PGB) in the Sea of Japan is simulated from a Lagrangian point of view based on the retrospective velocity field of the ROMS circulation model with horizontal resolution of 600 m. The particle-tracking experiments with the effects of oil evaporation and biodegradation have been performed releasing hourly passive tracers at the beginning of every month during a few years. These numerical experiments showed pathways of spilled oil in different seasons, size of the open-sea area covered by the oil and risks of coastline contamination. Three main scenarios of propagation of the spilled oil in the surface layer have been found and analyzed. In the first one, the spilled oil drifts fast away from the coast due to prevailing north/northwest winds in the cold season (from December to April). The second scenario predominantly occurs in the warm season (from May to November) with prevailing south/southeast winds when the oil slick remains near the coast in the first days after an incident. The third scenario is an intermediate one with the dispersal of the spilled oil away from the coast but not too far from the oil spill site. To explain this behavior, we used the Lyapunov maps which allowed us to identify Lagrangian fronts in the study area that shape passive tracer evolution. As a Lagrangian front moves, the oil slick moves with it. At the same time, the front acts as a transport barrier preventing cross-frontal spreading of oil. [ABSTRACT FROM AUTHOR]

Strong cold air outbreaks caused heavy snowfall over the inland areas of the Sea of Japan coast of Japan in mid‐December 2020. The 48‐hr accumulated snowfall during the term broke a snowfall record at some observational stations of the Japan Meteorological Agency (JMA). We investigated the impacts of atmospheric and oceanic temperature changes due to historical global warming since the pre‐industrial period on this heavy snowfall event. Hindcast and pseudo non‐warming experiments were conducted using the nonhydrostatic model developed by the JMA. The historical climatic differences were obtained from the database for policy decision‐making for future climate change (d4PDF). Our experiments indicated that historical global warming enhanced precipitation over the whole region and enhanced heavy snowfall over the inland areas on the Sea of Japan side. In this event, the contribution of conversion from snowfall to rainfall due to warming was limited over coastal areas. The enhancement of precipitation was mainly caused by oceanic warming, which increased latent heat flux over the Sea of Japan and made the low‐level atmosphere less stable. Historical atmospheric warming suppressed precipitation due to atmospheric stabilization. Our results indicated that the heavy snowfall was caused by the cold air outbreaks under the warm sea surface temperatures in December and enhanced by historical global warming. Plain Language Summary: Heavy snowfall occurs over the inland areas of the Sea of Japan coast in mid‐December 2020. The 48‐hr accumulated snowfall broke a snowfall record at some observational stations. The numerical simulations indicate that historical global warming since the pre‐industrial period enhanced the heavy snowfall over the inland areas on the Sea of Japan side. The oceanic warming is more important for the enhancement of snowfall than atmospheric warming only, because oceanic warming supplies more moisture to the atmosphere and makes the low‐level atmosphere less stable. Since the sea surface temperature in December is warmer than that in other month in winter, it widely enhances snowfall over the inland areas along the Sea of Japan. Key Points: Historical global warming enhanced heavy snowfall occurring over inland areas along the Sea of Japan in central Japan in mid‐December 2020Sensitivity experiments indicate that warming of the Sea of Japan mainly contributed to the enhancement of heavy snowfallOceanic warming supplies more moisture to the atmosphere and makes the low‐level atmosphere less stable, which enhances precipitation [ABSTRACT FROM AUTHOR]

The January 1, 2024 Noto Peninsula M w 7.5 tsunamigenic earthquake, with at least 241 deaths, was the most destructive event in Japan following the March 2011 M w 9.0 catastrophic event. We conducted field surveys in the affected area 24 days after the event to document tsunami heights, runups, coseismic coastal uplift and damage to coastal structures. Here, we present the results of the surveys and analyze tsunami height distribution and associated damage. In our survey of 29 locations, tsunami runups and heights varied in the ranges of 4.4–6.2 m, and 1.0–4.4 m, respectively. Notably, Joetsu, the farthest location from the epicenter in our field survey, recorded the highest runup of 6.2 m, which is attributed to the directivity effect of tsunami waves. The maximum surveyed runup of 6.2 m closely aligns with the reported maximum fault slip of 4–6 m for this earthquake, confirming a long-established rule of thumb. Coastal crustal uplifts of up to 1.6 m have rendered many ports unsuitable for use. We identified three failure mechanisms affecting coastal structures: overturning caused by tsunami backwash, damage resulting from tsunami inundation currents and wave pressure, and impacts from floating objects and debris. • Maximum runup of the Jan. 2024 Noto Peninsula (Japan Sea) tsunami was 6.2 m. • Coastal crustal uplifts of up to 1.6 m have rendered many ports unsuitable for use. • Maximum tsunami runup (6.2 m) was comparable to the maximum fault slip (4–6 m). • Three failure mechanisms observed: tsunami backwash, wave pressure, debris impacts. [ABSTRACT FROM AUTHOR]

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]

Pacific white‐sided dolphins, Lagenorhynchus obliquidens (PWSDs), migrate along the coast of Japan. PWSDs rarely emit whistles, instead utilizing pulses, unlike many other delphinid species that frequently emit whistle sounds. In the present study, we aimed to clarify the acoustic characteristics and repertoire of the whistle of PWSDs, which have not been reported so far. We analyzed PWSD whistle sound systems (e.g., acoustic parameters and contours) during boat surveys and using passive acoustic monitoring in shallow coastal waters in the northern Sea of Japan. PWSDs in Shakotan rarely emitted whistles, while the burst pulse frequently was as reported in previous studies in other waters. The PWSD whistle vocalization rates were higher during traveling than during foraging. The frequency and duration of their whistles did not appear to change between behaviors. Although complex multiloop whistles were not recorded, whistle contours were classified into seven types. Whistles are often recorded intensively in a short period as a sequence or bout. Considering the extremely low whistle vocalization rates, dolphins may choose whistles instead of pulsed sounds in limited contexts. Our results shed light on the differences in whistle sound usage within odontocete species. [ABSTRACT FROM AUTHOR]

This study summarizes the findings of an attitude survey focused on people's perceptions of seismic hazard maps, which illustrate the risk of an earthquake in each location throughout Japan. These seismic hazard maps depict the likelihood of an earthquake with a seismic intensity of "6 Lower" or more within 30 years, with 3.0% being considered a high possibility. The 3.0% occurrence probability within 30 years can be reworded to 2.0% occurrence probability within 20 years, 0.1% occurrence probability within a year, 4.9% occurrence probability within 50 years, or 39.4% occurrence probability within 500 years when being converted according to a Poisson distribution. In this study, we convert the occurrence probability within 30 years in the seismic hazard maps to obtain that within a year up to that within 1000 years, present the involved risk and demonstrate the yearly probability of the people who see the maps becoming most convinced of the need for countermeasures. Although those are shorter than the occurrence probability within 30 years anyway, it is a characteristic that the peaks existed at the occurrence probability within 10–20 years, not at the occurrence probability within one year or five years. However, the results changed according to the age of the people viewing the maps, and it was when the risk was presented as the occurrence probabilities within 20 and 30 years for the people in their 20–40 s, while it was when the risk was presented the occurrence probabilities within 10 years for the people in their 50–60 s, the perception toward the need of countermeasures increased the most. In addition, regardless of gender and place of residence (coast of the Sea of Japan or the Pacific coast), the perception toward the need of countermeasures peaked at the occurrence probabilities within 10 and 20 years. [ABSTRACT FROM AUTHOR]

Phylogeography infers the demographic history of various species by resolving genetic relationships among populations across a geographic range. Comparison of phylogeographic patterns of multiple species with similar geographic distributions, i.e., comparative phylogeography, allows us to assess the roles of regional historical events and species-specific ecological factors in shaping intraspecific genetic diversity, providing model systems for studying the processes and genetic basis of adaptive evolution and speciation. In addition, these patterns can also be compared among species from different regions to infer the impact of global-scale historical and present events, such as Pleistocene glacial cycles, on current biodiversity. In this review, I summarize and integrate recent findings of phylogeographic studies for two geographic lineages, Pacific Ocean (PO) and Sea of Japan (SJ) lineages, of five coastal gobies distributed around the Japanese Archipelago. Using mitochondrial and nuclear DNA markers, these studies revealed genetic divergences of the PO and SJ lineages in the coastal gobies. However, the two types of markers showed discordant patterns for genetic divergences between the two lineages (mitonuclear discordance), suggesting different coalescent processes between these genetic markers. Ecological features that depend on shallow coastal resources may contribute to restricted gene flow and be responsible for the existence of the two lineages that are predominantly found in the coastal gobies. All coastal gobies shared sharp contrasts in genetic diversity between the two lineages, with the SJ lineages rapidly expanding during Pleistocene interglacial periods. Such rapid population expansions can provide alternative ways to obtain recent calibration points to estimate divergence times of the two lineages. A comparison of the geographic distributions between the two lineages indicated that the centers of their secondary contact zones vary, which may appear to represent the continuous transition process of the two lineage distributions. Compared with results of phylogeographic studies from other oceans, multiple divergence times, sharply contrasting demographic histories, and two independent secondary contact zones are unique characteristics of the divergence between the PO and SJ lineages. These characteristics will allow us to test the continuous processes of genomic divergence during geographical isolation with environmental fluctuations and the consequences of hybridization of divergent lineages in independent secondary contact zones with different environmental settings. [ABSTRACT FROM AUTHOR]

Concentrations of 22 essential and non-essential trace elements (Be, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, Tl, Pb, Th, U, and Hg) were measured in the organs of a mother–fetus pair (at the last trimester of pregnancy) of spotted seals from the Sea of ​Japan. The concentrations of eleven elements are reported for the first time. Eight organs of the pair were examined: lungs, heart, liver, kidneys, intestines, spleen, muscles, and bones. All trace elements detected in the organs of the mother were found also in the organs of the fetus at various concentrations. Placenta is not an effective barrier to prevent non-essential elements from getting into the fetus, but can control entry of some of them, e.g., aluminum, cadmium, and mercury. In most organs of the fetus, the concentrations of toxic trace elements (beryllium, antimony, thorium, and uranium) were noticeably higher than in the same organs of the mother, which indicates that during pregnancy female removes excess of non-essential trace elements by transferring them to the fetal body through the placental barrier. [ABSTRACT FROM AUTHOR]

The evolution history of the Sea of Japan back-arc basin remains under debate, involving the opening of sub-basins such as the Japan and Yamato Basins. Detailed knowledge of the lithospheric structure will provide the key to understanding tectonic history. This study identifies the lithosphere–asthenosphere boundary (LAB) beneath the Sea of Japan back-arc basin using S-receiver functions (S-RFs). The study area, including the Japan and Yamato Basins, has been instrumented with broadband ocean-bottom seismometers (OBSs). S-RFs from these OBSs show negative Sp phases preceding the direct S arrivals, suggesting the LAB. The S-RFs also show abnormally reduced amplitudes. For further qualitative interpretation of these findings, we conduct transdimensional Bayesian inversion for S-wave velocity models. This less-subjective Bayesian approach clarifies that the low-velocity seafloor sediments and damped deconvolution contribute to the amplitude reduction, illuminating the necessity of such considerations for similar receiver function works. Inverted velocity structures show a sharp velocity decrease at the mantle depths, which we consider the LAB. The obtained LAB depths vary among sites: ~ 45 km beneath the Japan and Yamato Basins and ~ 70 km beneath the Yamato Rise, a bathymetric high between the two basins. The thick lithosphere beneath the Yamato Rise most likely reflects its continental origin. However, the thickness is still thin compared to that of eastern Asia, suggesting lithosphere extension by rifting. Notably, the Japan and Yamato Basins show a comparable lithospheric thickness, although the crustal thickness beneath the Yamato Basin is known to be anomalously thick. This consistency in the lithospheric thickness implies that both basins undergo similar back-arc opening processes. [ABSTRACT FROM AUTHOR]

The studied seep carbonates from Tsushima, Japan, are embedded within marine siliciclastics of the lower Miocene Taishu Group and represent the earliest evidence of hydrocarbon seepage in the Sea of Japan. In contrast to Miocene and Pliocene examples from Honshu, which are often found above anticlines, the seeps from Tsushima formed within a pull-apart basin before major anticlines had formed. The three carbonates from Fukuzaki, Kanoura and Tanohama are composed chiefly of calcite, with significant admixture of ankerite only at Kanoura. The stable carbon isotope composition of calcites (δ13C as low as −40.2 ‰ VPDB for Fukuzaki, −41.8 ‰ VPDB for Kanoura, and −52.8 ‰ VPDB for Tanohama) indicate methanogenic origin of the carbonates. Textures of these deposits, including radiaxial and yellow cements, are indicative of formation at a methane seep. The stable oxygen isotope composition of calcites (δ18O values as low as −14.4 ‰ VPDB for Fukuzaki, −14.5 ‰ VPDB for Kanoura and −13.9 ‰ VPDB for Tanohama) indicate that they were influenced by burial fluids. Burial diagenesis is also indicated by the stable isotopic compositions of ankerite (δ13C ranging from −19.1 ‰ to −7.1 ‰ VPDB, δ18O from −11.1 ‰ to −9.7 ‰ VPDB). Molecular fossils from Tanohama comprise n-alkanes with short-chain predominance, interpreted to have formed due to thermal cracking of organic matter. The carbonates yield a chemosynthesis-based community comprising vesicomyids Pleurophopsis chitanii, P. cf. hamuroi, the bathymodiolin 'Bathymodiolus' akanudaensis, the lucinid Lucinoma sp. and the provannid Provanna? sp., which have never been hitherto identified. 'Bathymodiolus' akanudaensis, Lucinoma sp. and Provanna? sp. are the oldest records of these taxa in the Sea of Japan. [ABSTRACT FROM AUTHOR]

The scale and age of extreme hydrological events that have been manifested over the past 2000 years on the coast of Valentin Bay is established based on stratigraphic study and radiocarbon dating of different facies deposits. The deposits of four major historical tsunamis (1993, 1983, 1644, and the 12th century) and a paleo-tsunami, which occurred between 1700–1800 cal yr BP. BP, were found. Sedimentation zones were mapped. The composition of diatoms in tsunami sands has been studied in detail. Along with marine and brackish water species tsunami waves also carried most freshwater forms that were redeposited from the coastal lake. Much of the material was supplied from depths up to 5 m. The correlation of events with data for the Japanese Islands is carried out. It has been suggested that the most dangerous tsunamis for this part of the Eastern Primorye coast are caused by submarine earthquakes with epicenters located near the Okushiri Island. The tsunamis associated with earthquakes with epicenters located near the northwestern Honshu Island, were less pronounced. Data on the irregular frequency of extreme floods during the last millennium has been obtained. It was established that the pluvial phase of the Warm Medieval Period ended in the early to mid-12th century. During the Little Ice Age, the water content of the rivers was insignificant, only two events, comparable to the catastrophic floods of the late 20th to early 21st century, are known to correspond to the warm phase of the mid-14th century to early 15th century. Only two of the modern floods have left traces recorded in the sedimentary sequences of the Valentin Bay coast. [ABSTRACT FROM AUTHOR]

During cruise 73 of the R/V Professor Gagarinskiy and cruise 53 of the R/V Akademik Oparin, oceanographic studies of the Sea of Japan and Sea of Okhotsk and the Northwest Pacific were carried out. New data were obtained on the seafloor structure, water structure, and slope convection features in the Sea of Japan. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) and polyethylene terephthalate (PET) are among the most abundant plastics polluting the oceans. However, their environmental fate depends on how they have been weathered. Due to its unique geography, the Sea of Japan is a pollution hotspot where plastics accumulate. In this study, the structures of plastics, having drifted into the Sea of Japan coastline environment, were analyzed with a particular focus on examining polymer crystallization and carbonyl formation; two factors which influence microplastic formation and the adsorption of contaminants onto plastic surfaces. PE in the coastal environment did not show evidence of crystallization, although carbonyl formation did increase. By contrast, PET bottles were shown to not be uniform in structure, with unaged bottles being less crystalline in the neck component compared to the body. Because of this difference, in environmental PET bottles, it was the bottle neck that showed increases in crystallization and carbonyl group formation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The subgenus Setihenricia Chichvarkhin and Chichvarkhina, 2017 currently consists of 32 out of 94 species of sea stars in the genus Henricia Gray, 1840. However, only 10 have been molecularly ascertained as to the phylogenetic position. Based on seven mitochondrial gene markers (16S rRNA, COI, tRNA-Ala, tRNA-Leu, tRNA-Asn, tRNA-Gln, and tRNA-Pro), we performed molecular analyses to assess the monophyly of Setihenricia using 16 species of Henricia from Japanese waters, as well as other congeners for which sequences were available in public databases. The monophyletic Setihenricia was only weakly recovered because the support values were low, but we assume this taxon may be valid in consideration of a morphological key. Henricia kinkasana Hayashi, 1940 is herein identified as a new member of Setihenricia, based on molecular and morphological evidence. Sequences in the public databases previously identified as H. compacta (Sladen, 1889) and H. obesa (Sladen, 1889) were nested in the Setihenricia clade; these two species are also likely members of Setihenricia . Our morphological assessment yielded three findings: (1) the number of the rows of spines on each inferomarginal plate, being three or more, appears to be a useful diagnostic character for Setihenricia, as has been suggested in previous studies, (2) the degree of spine tapering turned out to be less relevant in diagnosing the subgenus than previously supposed, (3) two newly introduced characters--( i ) the width of adambulacral plates and ( ii ) the ratio of two measurements in ambulacral plates to the length of interradius--may be effective to distinguish members of this apparent Henricia subclade from other members of the genus. [ABSTRACT FROM AUTHOR]

In 2017, 25 marine a nnelid s pecies (including u nidentified s pecies) of 16 families were collected from intertidal and shallow subtidal zones on Rishiri Island, northern Japan. Among collected specimens, 13 species of five families are new to the fauna of the island. A total of 79 annelid species in 23 families have been recorded from coastal areas of Rishiri Island. [ABSTRACT FROM AUTHOR]

The greater argonaut Argonauta argo is a species of the paper nautilus (Argonautidae), which is a family in Octopoda. In this paper, we report its full mitogenome sequence, which was obtained from a specimen collected in the Japan Seas near Oki Island, Shimane Prefecture, in Japan. The sequence was determined using the NGS Illumina HiSeq platform. With its 37 genes, the mitogenome shows a typical metazoan and Octopoda genomic structure, and similar to the mitogenome of the previously reported congener, A. hians. To confirm A. argo phylogenetic position in Octopoda, we conducted maximum likelihood phylogenetic analysis, using a data set including publicly available 17 Octopodiformes, five Decapodiformes, three Nautiloids and two outgroup Conchiferans. The result confirmed the affinity of Argonautidae to Tremoctopus, and the sister group position of this clade against the rest of incirrate Octopods. The mitogenome and phylogeny of A. argo reported here will be useful for future studies involving this enigmatic species, including on the reacquisition of external calcified shell structures in mollusks. [ABSTRACT FROM AUTHOR]

This publication presents the results of a study of the total mercury (THg) concentration in the fetal hair (lanugo) of the young spotted seals inhabiting the Peter the Great Bay, Sea of Japan. We analyzed samples from pups that were collected in 2014-2017 at the seal breeding grounds. The concentration of total mercury was determined by atomic absorption spectrometry. The concentration of THg ranged from 1.52 to 6.68 μg/g dry weight. Mercury concentration in the lanugo exceeds that found in the environment (bottom sediments, sea water) and in other animals inhabiting the Bay. At the same time, the level was generally lower than that found in young seals of most other pinniped species (Steller sea lion Eumetopias jubatus, Northern fur seal Callorhinus ursinus, Harbor seal Phoca vitulina richardsi, Northern elephant seal Mirounga angustirostris, California sea lion Zalophus californianus) from the North Pacific. [ABSTRACT FROM AUTHOR]

A mycological study of three major commercial bivalve species, Yesso scallop Mizuhopecten yessoensis, Pacific oyster Crassostrea gigas, and bay mussel Mytilus trossulus, from the coastal waters off Rikord Island (Peter the Great Bay, Sea of Japan) has been conducted. A total of 52 species of filamentous fungi from 19 genera of ascomycetes (and their anamorphic stages) and zygomycetes were isolated from shells and internal organs of the examined bivalves. Thirty-eight species (18 genera) of filamentous fungi were isolated from Yesso scallop, 21 species (eight genera) from Pacific oyster and 10 species (seven genera) from bay mussel. The studied bivalves showed a low degree of similarity in the diversity of the filamentous fungi. The identified filamentous fungi of the genera Aspergillus, Penicillium, Cladosporium, Chaetomium, etc. belong to a group of opportunistically pathogenic and toxigenic microorganisms that can cause mycoses and mycotoxicoses in aquatic animals. [ABSTRACT FROM AUTHOR]

The Japan Sea is directly influenced by the Asian monsoon, a system that transports moisture and heat across southeast Asia during the boreal summer, and is a major driver of the Earth's ocean‐atmospheric circulation. Foraminiferal and facies analyses of a 460‐kyr record from Integrated Ocean Drilling Program Expedition 346 Site U1427 in the Japan Sea reveal a record of nutrient flux and oxygenation that varied due to sea level and East Asian monsoon intensity. The East Asian summer monsoon (EASM) was most intense during marine isotope stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c when the Tsushima Warm Current flowed into an unrestricted well‐mixed normal salinity Japan Sea, whereas East Asian winter monsoon (EAWM) conditions dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level minima restricted the Japan Sea resulting in low‐salinity and oxygen conditions in the absence of Tsushima flow. Reduced oxygen stratified, low‐salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI when East China Sea coastal waters breached the Tsushima Strait. Chinese loess, cave, and Lake Biwa (Japan) and U1427 proxy records suggest EASM intensification during low to high insolation transitions, whereas the strongest EAWM prevailed during lowest insolation periods or high to low insolation transitions. Ice sheet/CO2 forcing leads to the strongest EAWM events in glacials and enhanced EASM in interglacials. Mismatches between proxy patterns suggest that latitudinal and land/sea thermal contrasts played a role in East Asian monsoon variability, suggesting that a complex interplay between ice sheet dynamics, insolation, and thermal gradients controls monsoonal intensity. Key Points: East Asian summer monsoon intensified in MIS 5, MIS 7, MIS 9, and MIS 11 when the Tsushima Current flowed into an unrestricted normal marine Japan SeaEast Asian winter monsoon dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level lows restricted the Japan Sea causing low‐salinity and oxygen conditionsReduced oxygen stratified, low‐salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI [ABSTRACT FROM AUTHOR]

Several stages are recognizable in landscape evolution along the Eastern Primorye coast, Kit Bay and its surrounding mountains in terms of climatic changes and related sea level fluctuations during the middle–late Holocene. The last 3.8–3.5 cal ka years were marked by a notable effect of the pyrogenic factor. The sea level rise at the maximum phase of the Holocene transgression led to the formation of lagoons at stream mouths, which underwent a complicated development. At that time, the coast’s principal topographic elements came into being, and the modern landscape’s pattern was laid on the coastal lowlands. The authors trace the changes in the vegetation in the process of short-term warmings and coolings. Korean pine appeared in the forests surrounding Kit Bay much earlier than in other regions of the Eastern Primorye. During the considered period, warmer phases were marked by increasing importance of broadleaf species, while at the cooler phases, a proportion of the Korean pine grew in the low mountains. In the last 2.3 cal ka, at greater elevations in the middle mountains, dark coniferous forests became more widespread, particularly spruce. At the same time, larch groves existed around the coastal sphagnum bog, probably due to seasonally frozen ground persisting for the greater part of a year. Extreme events with a considerable effect on the coastal landscape evolution include floods, whose frequency has been growing for the last 1.75 cal ka. Strong tsunamis are another factor influencing coastal evolution. Finally, changes in landscapes have been recorded related to human activities in the last few decades. [ABSTRACT FROM AUTHOR]

We investigated radiocesium concentrations in the suspended solids (SS) of two large rivers discharging into the Sea of Japan. Higher 134Cs concentrations in SS sampled from upstream area in 2013 (711 Bq/kg-SS) reflected the larger effect of radioactive depositions in western Fukushima Prefecture. However, smaller but less variable concentrations in downstream areas (< 100 Bq/kg-SS) indicated a continual supply of 134Cs-contaminated SS from 2013 to 2017. The particulate 134Cs concentrations in normal flow conditions were at approximately similar levels with those in coastal waters (< ~1 mBq/L), suggesting that the impact of SS on the Sea of Japan was negligible after 2013. [ABSTRACT FROM AUTHOR]

ABSTRACT Nakashita, S.; Woo, H.; Kim, K.; Kim, K.; Lee, I.-C.; Kim, D.-S., and Hibino, T., 2018. Influence of Kuroshio path on Salinity distribution in Seto Inland Sea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 21–25. Coconut Creek (Florida), ISSN 0749-0208. This study analyzes residual current and salinity distribution in Seto Inland Sea induced by Kuroshio Path variation. The salinity ranged 30 - 34 PSU and it decreased by approximately 1 - 2 PSU at near center of Bisanseto during non-meandering period. Sea level height variations at both boundary of Seto Inland Sea which induces residual current mainly depends on distance between boundaries and Kuroshio Path because of higher sea level hight at Kuroshio path than than that at northern part of Kuroshio path approximately 1 m. Westward residual flow during the non-meandering period (year 1997) was estimated to be faster than that during the meandering period with maximum relative velocity of 4.5 cm/sec. Decrease of salinity at near center of Bisanseto is due to the westward movement of the river water plume from the eastern Bisanseto. From the results obtained above, it is concluded that location of low salinity water at Bisanseto is mainly depends on the residual current due to variation of Kuroshio Path. [ABSTRACT FROM AUTHOR]

The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200–300 km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600 km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410–660 km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M > 7.0; depth > 500 km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related to the deep seismicity. However, many of these results are still preliminary, due to the lack of seismic stations in the Japan Sea. The key to resolving these critical geoscientific issues is seismic instrumentation in the Japan Sea, for which international cooperation of geoscience communities in the East Asian countries is necessary. [ABSTRACT FROM AUTHOR]

The Mohorovičić discontinuity (Moho) is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide. Moho depth varies regionally and remains a fundamental parameter of crustal structure. We present a new method of mapping the Moho using a 3D seismic tomography model. Since the tomographic method cannot locate discontinuities, we treat the Moho as a zone of high velocity gradient. Maximum lower crust/minimum upper mantle P-wave velocities in Japan are known to be 7.0 km/s and 7.5 km/s, respectively. We map the residual between isovelocity surfaces of 7.0 km/s and 7.5 km/s to find areas where the residual is small, the separation between the surfaces is narrow, and the velocity gradient is high. The Moho is best constrained where the isovelocity surfaces are close together, and under much of Japan, they are < 6 km and rarely > 10 km apart. We chose an isovelocity surface of 7.2 km/s as a representative Moho ‘proxy’ in these areas. Our resulting ‘Moho’ map under Japan compares favorably with existing regional Moho models that were obtained from controlled-source seismic investigations. The ‘Moho’ varies from shallow (25–30 km) to deep (> 30 km), and this variability relates to the structural evolution of the Japanese islands: the opening of the Sea of Japan back-arc, ongoing arc-arc collisions at the Hidaka and Izu collision zones, ongoing back-arc extension in Kyushu, and a possible failed back-arc extensional event of Mesozoic age. It is apparent that the Moho is less well-constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc-arc collision. [ABSTRACT FROM AUTHOR]

We evaluated fault activity in northeast-central Japan based on fault orientation, regional stress field, and slip tendency analysis for active and non-active faults (i.e. faults for which Quaternary activity has not been identified). Slip tendency is generally higher along active faults than non-active faults, although a high slip tendency was observed along some non-active faults, indicating their potential to become active. The potential for fault activity along non-active faults can be modeled using the temporal evolution from non-active to active during long-term crustal deformation. The density of potentially active faults varies spatially across the study areas and reflects the temporal evolution of crustal deformation in northeast-central Japan. [ABSTRACT FROM AUTHOR]

To study the environmental impact of the assessment technologies for the development of shallow methane hydrate zones in the Sea of Japan, deep-sea amphipods (Pseudorchomene sp. and Anonyx sp.) were collected from a depth of approximately 1000 m and were tested for H 2 S toxicity. At 0.57 mg L -1 H 2 S, all specimens of Pseudorchomene sp. were dead after 96 h, whereas all individuals survived at 0.18 mg L -1 . Moreover, Anonyx sp. had a survival rate of 17 % after 96 h at 0.24 mg L -1 . A similar toxicity test was conducted with the coastal amphipod Merita sp., a detritivore, and all individuals died within 24 h at 0.15 mg L -1 . These results suggested that compared with coastal detritivorous amphipods, deep-sea detritivorous amphipods, which also live near biomats with sediment H 2 S concentrations exceeding 10 mg L -1 , showed a higher tolerance to H 2 S., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

There is a dearth of knowledge regarding the spatiotemporal distribution of protistan community composition and seasonal environmental changes. High-throughput sequencing of the 18S rRNA gene was performed to assess changes in the community composition of protists over four seasons at four sites in Wakasa Bay, located in the center of Japan's northern coast. The community composition varied seasonally rather than geographically, even among few local communities confined to the bay head. Throughout the year, Alveolata and Chlorophyta were widely distributed and represented the predominant groups. Groups I and II of Syndiniales and Dinoflagellata were significant taxa in terms of operational taxonomic unit richness and sequence read abundance. Although three lineages of prasinophyte Clade VII, Pycnococcus -related prasinophyte, and Ostreococcus -related Mamiellophyceae were common, prasinophyte Clade VII was dominant during summer–autumn, whereas others were dominant during winter and spring. These results indicate the differential dominance of Chlorophyta at the intrataxon level. In the protistan community, increased temperature exerted an effect on the summer–autumn composition, whereas increased nitrate concentration showed an effect on the winter composition, suggesting that seasonal environmental changes affect the protistan community composition with different fluctuation patterns being observed among taxa. • 18S rRNA gene based HTS was analyzed in Wakasa Bay. • Season specific protistan community was detected. • Syndiniales group I and II and Chlorophyta were dominated. • Different taxa of Chlorophyta showed season specific dominance. • Temperature, nitrate and salinity were effective parameters on protistan community change. [ABSTRACT FROM AUTHOR]

In the middle of December 2014, a storm surge induced by explosive cyclone struck Nemuro, a city located in Hokkaido, Northern Japan, causing immense damage due to flooding. This explosive cyclone suddenly intensified along the east coast of Tohoku region and remained stationary near the Nemuro Bay due to the atmospheric blocking which existed over the Sea of Okhotsk. In this study, we analyze the moving velocity of explosive cyclones in 1960 to 1999 and they are compared with those of typhoons considered as another meteorological cause for storm surge. Furthermore, we discuss synoptic fields in which explosive cyclones move slowly in Northern Japan utilizing an atmospheric blocking diagnosis method. [ABSTRACT FROM AUTHOR]

Spatiotemporal variability of the internal gravity waves in the Sea of Japan shelf zone (in the Peter the Great Bay) is analyzed basing on the results of the experimental data processing. It is shown that, as for autumn water structure, the tidal internal waves moving towards the coast are transformed due to the non-linear effects and may reach significant amplitudes (of about 10 meters). Such waves are usually referred to as strongly non-linear. The main characteristics of such intense waves were estimated. An example of the disintegration of solitary temperature depression into the package of short-period intense internal waves is given. [ABSTRACT FROM AUTHOR]

The interlayers of the cryptotephra of different episodes of the catastrophic eruption of the Baitoushan volcano (Paektu-san, Changbaishan-Tianchi) in the 10th century were discovered in the sedimentary cover of Amur Bay in the Sea of Japan by the geochemical and paleomagnetic characteristics. The petrochemistry of the volcanic glass indicates the possible occurrence of pyroclastic material in the B-Tm layer and more recent episodes that have not been identified before in the sediments of the Sea of Japan. The impact of the eruption on the bay environment is noted. It is shown that the medieval state of Balhae occupying vast areas and adjacent to the volcano no longer existed after the more earlier episodes of eruption. [ABSTRACT FROM AUTHOR]

New data on geology, geochemistry, and isotope systematics of lavas in the East Sikhote-Alin area, along with earlier published evidence for the Sea of Japan, provide insights into the dynamics of back-arc basins and their role in the tectonic and magmatic history of continental margins. Right-lateral strike-slip faulting, the key event in the Cenozoic history of East Sikhote-Alin, apparently had no relation with the subduction in post-Eocene time. At that time, the Late Cretaceous subduction ended and oceanic asthenosphere with Pacific-type MORB isotope signatures injected into the subcontinental mantle through slab windows. The Sea of Japan opening began in the Eocene with formation of small rift basins in the Tatar Strait, which accumulated coastal facies. During the main Miocene phase of activity, the zone affected by oceanic asthenosphere moved eastward, i.e., to the modern deepwater Sea of Japan. The effect of oceanic asthenosphere on the continental margin ended in the Late Miocene after the Sea of Japan had opened and new subduction initiated east of the Japan Islands. [ABSTRACT FROM AUTHOR]

The East/Japan Sea (hereafter, the East Sea) is highly dynamic in its physical phenomena and biological characteristics, but it has changed substantially over the last several decades. In this study, a recent decadal trend of primary productivity in the East Sea was analyzed based on Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived monthly values to detect any long-term change. The daily primary productivities averaged using monthly values from 2003 to 2012 were 719.7 mg⋅C⋅m-2⋅d-1 (S.D. ± 197.5 mg⋅C⋅m-2⋅d-1, n = 120) and 632.3 mg⋅C⋅m-2⋅d-1 (S.D. ± 235.1 mg⋅C⋅m-2⋅d-1, n = 120) for the southern and northern regions of the East Sea, respectively. Based on the daily productivities, the average annual primary production in the East Sea was 246.8 g⋅C⋅m-2⋅y-1, which was substantially higher than that previously reported in deep oceans. However, a decreasing trend (13% per 10 years) in the annual primary production was observed in the East Sea within the study period from 2003 to 2012. The shallower mixed layers caused by increased temperature could be a potential cause for the decline in annual production. However, this decline could also be part of an oscillation pattern that is strongly governed by the Pacific Decadal Oscillation (PDO). A better understanding of primary productivity patterns and their subsequent effects on the marine ecosystem is required for further interdisciplinary studies in the East Sea. [ABSTRACT FROM AUTHOR]

Seasonal hydrochemical studies of the basic salt composition of water in the Partizanskaya R. estuary (Nakhodka Bay, the Sea of Japan), carried out in 2012, showed no within-year changes in the ratio of major ions, and hence the type of mineralization, in the river against a background of a pronounced seasonal variation of total mineralization. The mixing of river and sea water in the estuary is shown to be of a conservative character. [ABSTRACT FROM AUTHOR]

Data are presented on the chemical composition and the content of microelements including REEs in samples of pyrolusite, todorokite, and birnessite collected from a depth of 3500-3200 m by dredging a nameless elevation in the Central Basin of the Sea of Japan. The samples of pyrolusite are characterized by high hardness and density (3.35 g/cm). The conclusion of their hydrothermal genesis is made. [ABSTRACT FROM AUTHOR]

The article presents a case study of geochemical indicators for creation of typhoons in shelf sediments of Amur Bay of the Sea of Japan. It reports that sedimentary material brought by the Razdol'naya River acts as an indicator of paleo-typhoon. It highlights favorable factors for paleo-typhoon including low bioturbation of sediments due to ill treatment of benthic fauna and anoxic conditions of sedimentations.

Two sediment cores, KCES1 and ODP797, which were recovered from the Sea of Japan (JS), were measured for alkenone-derived sea surface temperatures ( $$U^{{\text{K}}^{\prime}}_{37} {\text{-SSTs}}$$ ). Our results revealed that the SSTs closely follow the glacial-interglacial cycles during the last 170 ka, except in the last glacial maximum (LGM), during which the SST was higher than in the Holocene. The anomalous high temperature in the LGM is considered as an effect of the intrusion of a low salinity water mass into the JS when the sea level was almost below 130 m. On the glacial-interglacial to orbital timescale, the $$ U^{{\text{K}}^{\prime }}_{37} {\text{-SSTs}} $$ record in the JS correlated well with the benthic foraminiferal δO record and solar insolation, which suggests the dominant control of solar insolation and its related sea ice development on the SST in the JS. On the sub-orbital/millennial timescale, reduced SST corresponds to an enhanced east asian winter monsoon (EAWM) during the last glacial period (MIS3 and MIS4), indicating the dominant control of sea ice expansion due to the enhanced EAWM on the SST in the JS. In contrast, during the last interglacial period (MIS5), the SST in the JS was controlled by variations in the east Asian summer monsoon. These results highlight the key role of solar insolation and associated glacial-interglacial conditions in the variations of the SST in the JS since the last 170 ka. [ABSTRACT FROM AUTHOR]

Concentrations of 13 phase-partitioned polycyclic aromatic hydrocarbons (PAHs) in seawater were monitored monthly off Oki Island, Japan, during 2015–2019 to elucidate seasonal variations, main source, and transport pathways of PAHs in the southwestern Sea of Japan. Total PAH (dissolved plus particulate) concentrations in surface seawater at 36°09.0′N, 133°17.3′E (site OK) were in the range 0.49–9.36 ng L−1 (mean 2.77, SD 2.05 ng L−1) with higher levels in summer–autumn, an order of magnitude lower than those in the East China Sea during 2005 and 2009–2011 and about one-third of those recorded in the Sea of Japan in 2008 and 2010. The main sources of dissolved and particulate PAHs were combustion products. Increasing dissolved PAH levels during July–October indicate that the area around southern Oki Island is impacted by PAH-rich summer continental-shelf water transported by the Tsushima Warm Current flowing from the East China Sea. • PAHs in surface seawater exhibited seasonal variation with high levels in summer–autumn. • Combustion products are the primary PAH source for surface seawater. • Seawater is impacted by PAH-rich summer continental-shelf water from the East China Sea. [ABSTRACT FROM AUTHOR]

The Taishu Group, a marine formation with a thickness of >5400 m, crops out on Tsushima Island, located in the southwestern Japan Sea. The group, which is generally regarded as early Eocene to early Miocene in age, provides important information about the tectonic setting of the Japan Sea. In this study, we present new SHRIMP U- Pb dates for igneous zircons from the Kunehama Tuff, which is in the basal part of the Taishu Group, and the Oobaura Tuff, which is in the uppermost part of the group. Results show that the Taishu Group was deposited rapidly, during the short interval of 17.9-15.9 Ma (early-middle Miocene), and is equivalent to other early-middle Miocene strata found in the Japan Sea region. Our results provide new constraints on the geological history of the Japan Sea and its islands. [ABSTRACT FROM AUTHOR]

Abstract: We studied diatom assemblages and CaCO3 contents of methane-derived authigenic carbonates from the eastern margin of the Sea of Japan and assessed the formation time of these samples. Radioactive 14C date was determined in selected samples to obtain the maximum age of the time. The results of our study suggest mass formation of carbonate nodules in a glacial period within ∼40 ky, consistent with a published U/Th dating result of carbonate nodules in the study area. Diatom assemblages and contents in the carbonate nodules (abundance of ∼106/g, dominance of neritic-littoral species, warm/cold water species ratio lower than ∼25) differ from the near-seafloor sediments in the study area, which have characteristics of Holocene sediments in the Sea of Japan, and suggest cementation of glacial sediments. Laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi-enclosed ocean. Similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules. Glacial sediments with oceanic cold water species as low as Holocene sediments restricts the sediment age to before 20 cal. ky BP. Carbonate contents higher than 78 wt% suggest the cementation of poorly compacted sediments near the seafloor, and the date of carbonate cementation is, therefore, close to that of the cemented sediments. Most carbonate nodule samples in this study were formed in a glacial period and detection of 14C restricts this period to within ∼40 ky. [Copyright &y& Elsevier]

Abstract: We present new compositional data on glass shards from cryptotephra layers in five marine sediment cores from the southern Japan/East Sea. The hand-picked glass shards were extracted from cryptotephra horizons that were distinguished by SEM/EDS for major elements and INAA for trace elements on individual shards. Most of the glass shards have alkaline and trachyte–phonolite compositions, and have major and trace element compositions similar to eruptive units on Ulleung Island. Stratigraphic inferences indicate the presence of at least four alkaline tephras, U-3, Post-U–Oki, U–Oki, and Pre-U–Oki in the interval between the K–Ah rhyolitic tephra (7.3calka BP) and the TL1 regional dark sediment layer (11.8calka BP). The new trace elements on glass shards indicate minor compositional distinctions from one visible tephra and four cryptotephras that help to infer fine-scale regional correlations. The development of a more comprehensive alkaline tephrostratigraphical framework for this region will greatly aid in the reconstruction and chronology of regional stratigraphic variations. The recognition of new alkaline cryptotephras in the marine sediments of the Japan/East Sea also contributes towards a better understanding of the volcanic history of Ulleung Island and nearby seamounts. [Copyright &y& Elsevier]

Trace metals play an important role in marine biogeochemistry. However, the detailed distribution of trace metals in the Seas of Japan and Okhotsk remain unknown. Herein, we report the full-depth and section distributions of the dissolved (d), total dissolvable (td), and labile particulate (lp) phases of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in seawater samples collected from the Seas of Japan and Okhotsk during the GEOTRACES-Japan program. High lpM/tdM ratios suggest active scavenging in the Seas of Japan and Okhotsk. The lpAl and lpFe species were dominant in tdAl and tdFe, showing a strong positive correlation to each other in the both the Seas of Japan and Okhotsk. The maximum lpAl, lpFe, lpMn, and lpCo concentrations were observed at σ 0 = 26.8–27.0 for dense shelf water (DSW) in the Sea of Okhotsk, implying that a metal source is laterally transported to the western subarctic North Pacific. The high enrichment factors of dMn, dCo, dNi, dCu, dZn, dCd, and dPb in the surface water of the Sea of Japan were attributed to anthropogenic emissions of these metals. In addition, temporal variations of the trace metals were examined in the Sea of Japan. The distribution of dCd did not change significantly during 1984–2010; however, data suggest that lpMn and lpFe exhibited dynamic temporal and spatial variations. • Trace element distribution and stoichiometry in the Seas of Japan and Okhotsk studied. • Al and Fe are dominated by labile particulate species with a strong correlation. • Shelf water of the Sea of Okhotsk is a source of Mn, Fe, and Co to the Pacific Ocean. • Anthropogenic metals are enriched in surface water of the Sea of Japan. • Dissolved Cd profiles are consistent between 1984 and 2010 in the Sea of Japan. [ABSTRACT FROM AUTHOR]

Wind turbines on the coast of the Sea of Japan have been damaged by lightning in winter. This is due to the frequent occurrence of upward lightning from wind turbines in winter. Occurrence of upward lightning proves to be closely related to the temperature distribution at high altitudes. In this paper, the correlation between lightning hits of wind turbines and the height of the-10 °C layer is analyzed. When an upward lightning hits a wind turbine in winter, the height of the-10 °C layer is lower than 2000 m in most cases. Moreover, winter lightning is classified into two types, namely, the storm type and the inactive type, and it is found that the parameters of lightning currents observed by LLS differ depending on the type of lightning storm. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 44-50, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22357 [ABSTRACT FROM AUTHOR]

Abstract: Observations show that the maximum transport for the Tsushima Current (TC) through the Korea Strait occurs in autumn. For the TC, variation in transport changes the physical properties of the water as well as the distribution of nutrients, plankton, and other materials in the Japan/East Sea. Despite the importance of the TC, research is yet to unravel the cause of the maximum transport for the TC in autumn. In this study, observational data and numerical modeling data were analyzed in an effort to explore this phenomenon. The maximum transport through the Korea Strait was determined to be the result of the maximum onshore transport crossing the shelf break in the East China Sea (ECS); this transport is driven by strong northeasterly wind stress. Ekman transport driven by wind in the ECS is the primary cause of the maximum transport for the TC through the Korea Strait in autumn. [Copyright &y& Elsevier]

Abstract: The vertical and horizontal distributions of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP), together with dissolved inorganic nitrogen (DIN), phosphorus (DIP), silicate (DSi), and photosynthetic pigments, were measured in the euphotic layer (0–100m) along the south–north transect of the East/Japan Sea (EJS) in May 2007. In the mixed layer, the DIN concentrations were lower than 3μM, and the DIN:DIP ratios were lower than 10. Under this DIN-limited condition, cyanobacteria (20–65%) and diatoms (20–50%) dominated the phytoplankton community. The concentrations of DOC (60–83μM) and DOP (0.1–0.4μM) in the EJS fell into a range similar to those found in the major oceans, whereas the concentration of DON (2–7μM) was lower than that in the Pacific Ocean (7–13μM). The correlation analyses showed that the distributions of DOC, DON, and DOP in the study region were affected mainly by the physical characteristics of water masses. The lower DON concentrations, higher DOC:DON ratios, and lower DON:DOP ratios in the EJS, relative to the major oceans, together with a strong negative correlation between the concentrations DON and zeaxanthin, suggest that DON is preferentially taken up by cyanobacteria in this environment. Thus, our results show that the C:N:P stoichiometry of dissolved organic matter (DOM) in the EJS is controlled mainly by the physical and biological characteristics of water masses. [Copyright &y& Elsevier]

Long-term temporal variations of plutonium in Sea of Japan (SOJ) surface waters have been examined with the aim to better understand its behavior during several decades. The first observation is that 239,240 Pu activity concentrations in surface waters of the SOJ during 1977-2019 were 6.5 ± 4.7 mBq m -3 in average, and 5.1 mBq m -3 as the median, whereas 137 Cs and 90 Sr activity concentrations decreased with time, except of the perturbation due to the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Another observation is that sporadic high 239,240 Pu activity concentrations occurred in the east Japan Basin, ranging from 1 to 39 mBq m -3 . The spatial distribution of 239,240 Pu activity concentrations in surface waters revealed that high 239,240 Pu levels (>20 mBq m -3 ) occurred in 1994 in the northern SOJ, which was considered to be due to winter convection. To elucidate factors controlling the temporal variability of surface 239,240 Pu levels in the SOJ, a relationship between surface 239,240 Pu activity concentrations and vertical diffusion coefficients was examined. The results revealed that this relationship could be classified into two groups: one group did not show a change with increasing diffusion coefficient, while the other group showed a positive correlation. The vertical 239,240 Pu distribution in SOJ waters suggests that the high surface 239,240 Pu levels occurred due to the upwelling of cyclonic eddy. The rapid recycling of deeper plutonium occurred in the SOJ due to deep winter convection and upwelling associated with cyclonic eddy. The plutonium levels in the SOJ have been found to be sensitive to climate changes. Warming of the SOJ may cause a reduction of winter convection and eddy activity as a result of increasing sea surface temperature. This leads to a decline of recirculation of plutonium and other bioavailable elements from Japan Sea Proper Water (JSPW) to surface water layers. Plutonium would be, therefore, an important indicator of biogeochemical processes in the marine environment, helping to assess climate change impacts on marine ecological systems., (Copyright © 2022 Elsevier Ltd. All rights reserved.)