Japan Sea Coast Research Articles

Citizen Science Observation of a Gamma‐Ray Glow Associated With the Initiation of a Lightning Flash

AbstractGamma‐ray glows are observational evidence of relativistic electron acceleration due to the electric field in thunderclouds. However, it is yet to be understood whether such relativistic electrons contribute to the initiation of lightning discharges. To tackle this question, we started the citizen science “Thundercloud Project,” where we map radiation measurements of glows from winter thunderclouds along Japan's sea coast area. We developed and deployed 58 compact gamma‐ray monitors at the end of 2021. On 30 December 2021, five monitors simultaneously detected a glow with its radiation distribution horizontally extending for 2 km. The glow terminated coinciding with a lightning flash at 04:08:34 JST, which was recorded by the two radio‐band lightning mapping systems, FALMA and DALMA. The initial discharges during the preliminary breakdown started above the glow, that is, in vicinity of the electron acceleration site. This result provides one example of possible connections between electron acceleration and lightning initiation.

Testing the potential of Serpulidae tubes as an indicator of past relative sea-level collected from shored wave dissipating blocks along the Pacific and Japan sea coast of northeastern Japan

Relative sea-levels (RSL) in the past can be used to understand crustal movements, as paleo-shoreline elevations can be modified by seismic activities [1]. To assess short-term crustal movements, reliable RSL proxies are key in age determination to derive precise tectonic activities. The Tohoku region in northern Japan has complex oceanographic setting since two currents, cold Oyashio and warm Kuroshio being merged in the region. Here, we assessed the potential of Hydroides ezoensis (HE), as a new proxy of RSL. The 14C concentrations of HE collected in the Tohoku region were measured and compared with previous studies that reported radiocarbon values of the surface ocean. Results showed HE possesses summer surface 14C. This suggests that HE is suitable to be used as a reliable RSL proxy that can reliably provide age information without having influences from radiocarbon depleted Oyashio. Thus, HE could be used as a reliable proxy to understand paleo-RSL.

Possible northern persistence of Siebold's beech, Fagus crenata, at its northernmost distribution limit on an island in Japan Sea: Okushiri Island, Hokkaido.

Siebold's beech, Fagus crenata, is widely distributed across the Japanese Archipelago and islands in Japan Sea. Similar to the northern limit of the geographical distribution of F. crenata on the mainland of Hokkaido, the northern limit of the distribution of F. crenata on islands in the Japan Sea is observed on Okushiri Island (ca 42°N). To understand the genetic relationships of F. crenata on Okushiri Island, we examined chloroplast (cp) DNA haplotypes and 11 nuclear microsatellite (SSR) loci among 1,838 individuals from 44 populations from Okushiri Island, mainland Hokkaido, and the northern part of the Tohoku region on Honshu Island. We identified 2 cpDNA haplotypes, which represent not only populations on the Japan Sea coast but also those on the Pacific coast and this suggested the Okushiri Island populations might not be formed by single colonization. Genetic diversity of the Okushiri Island populations of nuclear SSR was not lower than the mainland and the STRUCTURE analysis revealed the Okushiri Island individuals were admixed between Hokkaido and Tohoku clusters. Approximate Bayesian computation inferred that divergence between Tohoku and Hokkaido, and admixture between two populations which generated Okushiri populations occurred before the last glacial maximum (LGM), that is, 7,890 (95% hyper probability density (HPD): 3,420 - 9,910) and 3,870 (95% HPD: 431- 8,540) generations ago, respectively. These inferences were well supported by a geological history which suggested an isolation of Okushiri Island from Hokkaido started prior to the Middle Pleistocene. We discuss the possible persistence of F. crenata during the last glacial maximum on northern islands in the Japan Sea such as Okushiri Island.

Subduction-related mantle accretion and makeover revealed by mantle xenoliths at the Pacific margin of NE Eurasia

Subduction is thought to be a major factor in the origin and makeover of continental lithospheric mantle, but essential aspects of these processes continue to be debated. Here, we report textural, chemical and Re Os isotope data on mantle xenoliths from far eastern Russia located at different distances from the Asian Pacific coast to examine how the proximity to subduction zones affects lithospheric mantle compositions. The xenoliths come from the Khanka block close to the border with China and several sites in the Sikhote-Alin orogenic belt (SAOB) near the Japan Sea coast. The inboard Khanka xenoliths are spinel lherzolites with chemical compositions, suggesting that they are residues of low- to moderate-degrees of melt extraction from fertile mantle and essentially unaffected by later events for 1.9 Ga. Such rocks are also common among peridotites in the SAOB, located closer to the subduction margins, but the SAOB suite also includes: a) heterogeneous rocks with veins and patches of pyroxenites or hydrous minerals, and b) rocks enriched in iron (8.8–13.5 wt%), Al 2 O 3 and incompatible minor elements. The positive correlation between elevated 187 Os/ 188 Os ratios (>0.135) and FeO contents in some Fe-rich SAOB xenoliths is interpreted to indicate that the metasomatic melts were derived from the asthenosphere hybridized with recycled materials from the Pacific slab. The lack of correlation between Re -depletion Os model ages (T RD ) and depletion indices, as well as the similarity of Os isotopic compositions between the SAOB peridotites and abyssal peridotites are interpreted to show that the SAOB mantle possibly formed and accreted to Eurasia from the asthenosphere during eastward migration of the Paleo-Pacific subduction trench. Based these results, we infer that the SAOB lithospheric mantle experienced multi-stage metasomatism after its formation, the most significant of which is localized infiltration of subduction-related basaltic melts with recycled characteristics induced by the extension of Japan Sea and release of volatiles from the slab. By contrast, the inboard Khanka lithospheric mantle shows little, if any, evidence for metasomatism. Such contrasting metasomatic modification implies different degrees and styles of makeover processes at different distances relative to the subduction margins. • The Khanka mantle was little affected by metasomatism since it was formed at ~1.9 Ga. • The Sikhote-Alin lithospheric mantle was formed by subduction and accretion. • Mantle metasomatism beneath Sikhote-Alin was caused by melts with recycled signature. • The nature and degrees of metasomatism are related to the distance from subduction front.

Geological record of 18th and 19th century tsunamis along the Japan Sea coast of Tsugaru Peninsula, northwestern Japan

Our stratigraphic and paleontological investigations revealed three sandy event deposits (E1, E2, and E3) within peaty clay at the Sotomeyachi site on the Japan Sea coast of Honshu (mainland of Japan), northwestern Japan. Visual examination and X-ray computed tomographic images of samples of the deposits provided evidence of strong currents characterized by rip-up mud clasts, load casts, and erosional lower stratigraphic contacts. Marine, brackish, and freshwater diatom species in the deposits indicate they were derived from various coastal sources. Radiocarbon dating constrained the ages of event deposit E2 to 1764–1902 CE and E3 to 1558–1845 CE, 1699–1918 CE, and 1704–1781 CE. According to historical records, the E2 deposits likely correspond to the tsunami generated by the 1833 Shonai-oki earthquake, and the E3 deposits correspond to a tsunami associated with either a submarine landslide associated with the 1741 Oshima-Oshima eruption or the 1793 Nishi-Tsugaru earthquake. Because our numerical simulation of the 1741 tsunami showed no significant inundation at the study site, it is more likely that the 1793 earthquake was responsible for tsunami deposit E3. The E1 deposit is discontinuous and showed different characteristics (absence of load structures, rip-up mud clasts and mixed diatom assemblages) to those of events E2 and E3, so it is unlikely to be a tsunami deposit.

LONG-RANGE ATMOSPHERIC TRANSPORT OF RADON IN EAST ASIA AND DEPOSITION OF ITS PROGENIES IN JAPAN.

A three-dimensional long-range atmospheric transport model for 222Rn and its progenies was applied to simulate 210Pb deposition in Japan and its adjacent waters. Monthly precipitation and 210Pb deposition simulated by the model for winter months were favorably compared with observational data although they were exceptionally underestimated in Aomori. The large monthly deposition along the Japan Sea coast lines during winter was successfully simulated by the model to be nearly 200Bqm-2, which was contrasted by about 10-fold smaller deposition in other regions. It was also pointed out that the heavy deposition areas formed a narrow band structure along the coastline with width of several tens of kilometers and 210Pb deposition amount positively correlated with the height of mountains located leeward of the heavy deposition areas.

Geodetic and Geological Deformation of the Island Arc in Northeast Japan Revealed by the 2011 Tohoku Earthquake

Northeast Japan is a typical island arc related to the Pacific plate subduction. The 2011 Mw9.0 Tohoku-oki earthquake provided a unique opportunity to analyze crustal deformation with different boundary conditions, similar to a gigantic rock deformation experiment. We review findings obtained through various observations and data analyses in Northeast Japan, focusing on the crustal deformation in different timescales. The occurrence of the M9 earthquake solved the ongoing paradox that the geodetic strain rate is an order of magnitude larger than the geologic estimate, showing that the centennial geodetic observation had mainly captured the elastic strain accumulation. Along the localized contraction zone along the Japan Sea coast, a comparison of postseismic and interseismic deformation patterns revealed a significant contribution of inelastic deformation, which plays an essential role in long-term deformation. Along the Pacific coast, rapid interseismic subsidence and unexpected coseismic subsidence were followed by a rapid postseismic uplift, indicating that viscous relaxation in the mantle is of essential importance. These findings advance our understanding of plate interactions and the tectonic evolution of the island arc. ▪ The 2011 Tohoku-oki earthquake provided the most complete crustal deformation data set ever for interseismic, coseismic, and postseismic periods. ▪ The discrepancy between the geologic and geodetic deformation rates in Northeast Japan is attributed to an elastic strain due to interplate locking. ▪ A significant contribution of inelastic deformation in the island arc crust is identified through a comparison of interseismic and postseismic deformations.

Possible dispersal of the coastal and subterranean carabid beetle Thalassoduvalius masidai (Coleoptera) by ocean currents

Abstract The spatial genetic structures of insects are reflected in their habitats. Coastal insects tend to have less genetic differentiation than subterranean insects. However, the general pattern of population structure of coastal species residing in subterranean habitats is unknown. Thalassoduvalius masidai (Coleoptera: Carabidae: Trechinae), endemic to Japan, is a coastal and subterranean beetle. Here, we hypothesized that T. masidai populations disperse among regions by ocean currents, floods and tsunamis, despite their habitat being underground. To test this hypothesis, we performed a phylogeographical analysis of T. masidai using single nucleotide polymorphism data from multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq) and the mitochondrial COI gene. The phylogenetic network and tree and STRUCTURE analyses indicated that T. masidai populations were divided into three groups: the western Seto Inland Sea–Izu Peninsula coasts, the eastern Seto Inland Sea–Kii Peninsula coasts and the Japan Sea coasts. The genetic diversity of T. masidai was higher in sites with lower longitude and latitude. These results suggest that T. masidai migrated and dispersed from the south-western area of Japan by ocean currents, despite its underground habitat. The genetic analysis data from the present study would also be helpful for the conservation and taxonomic revision of this species.

Hydraulic Evaluation of the Levee System Evolution on the Kurobe Alluvial Fan in the 18th and 19th Centuries

The development process and flood control effects of the open-levee system, which was constructed from the mid-18th to the mid-19th centuries, on the Kurobe Alluvial Fan—a large alluvial fan located on the Japan Sea Coast of Japan’s main island—was evaluated using numerical flow simulation. The topography for the numerical simulation was determined from an old pictorial map in the 18th century and various maps after the 19th century, and the return period of the flood hydrograph was determined to be 10 years judging from the level of civil engineering of those days. The numerical results suggested the followings: The levees at the first stage were made to block the dominant divergent streams to gather the river flows together efficiently; by the completed open-levee system, excess river flow over the main channel capacity was discharged through upstream levee openings to old stream courses which were used as temporary floodways, and after the flood peak, a part of the flooded water returned to the main channel through the downstream levee openings. It is considered that the ideas of civil engineers of those days to control the floods exceeding river channel capacity, embodied in their levee arrangement, will give us hints on how to control the extraordinary floods that we should face in the near future when the scale of storms will increase due to the global climate change.

Cross‐shore distributions of peracarid crustaceans after changes in beach morphology: The importance of suction as a key geoenvironmental variable

AbstractRecently, it has been shown that suction, which means the tension of moisture in sediments, is responsible for the distribution limits of the amphipods Haustorioides japonicus and Trinorchestia trinitatis and the isopod Excirolana chiltoni. Such effects take place through three distinctive suction‐induced mechanisms, associated with burrowing, physiology and the stability of burrows. Based on this background, in this study, we investigated storm‐induced morphological changes in beach profiles and the associated variations in geoenvironments, namely the suction, the degree of saturation, water content and sediment hardness, of the sandy beach habitats. The associated changes in cross‐shore distributions of the three peracarid crustaceans were also investigated. Field studies were carried out before and after monsoonal storms at two sandy beaches, Maze and Gokahama, located on the Japan Sea coast in Niigata Prefecture, Japan. The results showed that the suction‐induced variations of the geophysical environments were universal, irrespective of the storm‐induced morphological changes in the beach profiles. In addition, there were distinct changes in the cross‐shore distributions of the peracarid crustacean populations, associated with the storm‐induced morphological changes. The variations in the developed suction consistently and quantitatively accounted for these distinct changes in the cross‐shore distributions of the peracarid crustaceans, associated with the event‐induced morphological changes. Hence, suction played a crucial role as a key geoenvironmental variable in determining the distribution changes of the three peracarid crustaceans studied, even following the event‐induced morphological changes of the beach profiles.

Productivity and thallus toughness trade‐off relationship in marine macroalgae from the Japan Sea

SUMMARYTrade‐offs are considered key to understanding mechanisms supporting the coexistence of multiple plant species. Thus, understanding the mechanisms underlying trade‐offs is expected to contribute to conservation and management of macroalgal beds composed of diverse macroalgae of rocky shore ecosystems. To test the occurrence of trade‐offs between productivity and thallus toughness as well as pair‐wise thallus trait relationships that are expected to indirectly relate to any trade‐offs, traits and relationships for 13 species of macroalgae from the central area along the Japan Sea coast of Honshu, Japan were examined. In each species we examined for photosynthetic capacity per unit biomass (as Amass) and nitrogen (i.e., photosynthetic nitrogen‐use efficiency, PNUE), nitrogen content (as Nmass), thallus mass per unit thallus area (as TMA) and force required to penetrate the thallus (as Fp, a common index of leaf toughness in land plants by punch test). A significant negative correlation indicating a trade‐off between productivity and thallus toughness was found between Amass or PNUE and Fp. Pair‐wise relationships that were expected to indirectly relate to the trade‐off were as follows. Amass was positively correlated with Nmass. Thalli with high Nmass extensively utilizing nitrogen in the photosynthetic parts, and consequently exhibiting elevated metabolic rates. Moreover, thalli with high Nmass tended to be associated with low TMA, and Nmass decreased with increasing TMA. A significant negative correlation was observed between TMA and Amass or PNUE because of the linkage of high Amass or PNUE with high Nmass and high Nmass associated with low TMA, while a significant positive correlation was observed between TMA and Fp. The two correlations indicate a physiological and structural trade‐off, which underlies the interdependency of thallus traits. Results of multivariate analyses also indicated that the thallus traits interdependently vary across a single axis based on the trade‐off.

Estimating sedimentary environment of a Pleistocene sediment in Kyotango City, Kyoto Prefecture, Japan, with the first report of <i>Pseudopodosira kosugii</i> from the Pleistocene series on the Japan Sea Coast

Estimating sedimentary environment of a Pleistocene sediment in Kyotango City, Kyoto Prefecture, Japan, with the first report of <i>Pseudopodosira kosugii</i> from the Pleistocene series on the Japan Sea Coast

Single- and Dual-Doppler Radar Analysis of Misovortices within Snowband in Japan Sea Coastal Region on 17 January 2017

Single- and Dual-Doppler Radar Analysis of Misovortices within Snowband in Japan Sea Coastal Region on 17 January 2017

Hearing Survey from Fishermen Concerning Seaweed Communities on the Japan Sea Coast of Aomori Prefecture, Japan

Hearing Survey from Fishermen Concerning Seaweed Communities on the Japan Sea Coast of Aomori Prefecture, Japan

Environmental factors affecting benthic invertebrate assemblages on sandy shores along the Japan Sea coast: implications for coastal biogeography

AbstractAssemblages of sandy shores are primarily structured by physical environment factors. This structuring provides a unique opportunity to evaluate biogeographic regions. In this study, the shallow subtidal zone (0.2–1.2 m) of 39 sites of sandy shores along the Japan Sea coast of Honshu were surveyed using a sledge net to identify invertebrate assemblages and to elucidate their relationships with environmental factors and geographic distributions. In total, 78 taxonomic units were obtained and six clusters of assemblage were recognized according to the Morisita‐Horn dissimilarity index values between the assemblages of these sites. Indicator taxonomic units were identified for the clusters and a distance‐based redundancy analysis (dbRDA) demonstrated that a set of five environmental factors (slope angle of the swash zone, sediment grain size, average wave fetch, spring sea surface temperature, and summer Chlorophyll‐a concentration) significantly explained variations of the assemblages. Geographical distributions of two of the clusters were localized and mutually exclusive (one in the north and one in the south), while the other four clusters were scattered along the coast. On the dbRDA ordination, these two clusters were plotted on opposite ends of the 1st axis on which spring sea surface temperature and summer Chlorophyll‐a concentration showed high contributions. The spatial gap between the two clusters was located in an area between the Noto Peninsula and the Sado Island, central Honshu, which can be proposed as a boundary of geographic regions of sandy shore organisms along the Japan Sea coast.

Seasonality and Geographical Distribution of Tsutsugamushi Diseases in Japan: Analysis of the Trends since 1955 till 2014.

Data concerning the seasonality and geographical location of tsutsugamushi disease (TD) in Japan from 1955 to 2014 were compiled. After disappearance of "classical" TD in the mid-1960s, there was a long near-vacuum. Then, in 1975, a TD epidemic with October-December seasonality emerged in southern prefectures, and in 1979, that with May-June seasonality in northern prefectures. The current TD epidemic could be classified according to seasonality and geography into three types: a large October-December epidemic with a negligibly small May-June epidemic in the southern part of Japan, a large May-June epidemic with a mid-sized October-December epidemic on the Pacific coast of northern Japan, and a large epidemic in May-June with a negligibly small October-December epidemic on the Japan Sea coast of northern Japan. In addition, there were a few patients that were scattered throughout the year in various places in Japan. How these different epidemic patterns emerged is discussed.

Growing depth limit of Zostera caulescens in coastal waters along the Japan Sea coast of Honshu, Japan

There is a possibility that deep coastal marine macrophytes will be less critically affected by thermal stress associated with climate change and remain as refugia. Thus, information on them is expected to contribute to conservation of biodiversity in coastal areas affected by climate change. To document the deep-growing Zostera caulescens in relation to the light environment, field surveys were conducted in coastal waters of the central area along the Japan Sea coast of Honshu, Japan, and then the relationship between the light environment and seagrass depth limit was examined. In the coastal waters of Sado Island and Noto Peninsula, the presence of deep coastal communities of Z. caulescens was confirmed in the depth range of 20–25 m. Biomass and shoot density for Z. caulescens, ranging 34.1–51.3 g DW m−2 and 83–112 shoots m−2, were recorded at a depth of 20 m in Ryotsu Bay, Sado Island. For the genus Zostera including the deep-growing Z. caulescens, the relation between the extinction coefficient and seagrass depth limit was described by the fitted regression equation. The minimum light requirement of the deep-growing Z. caulescens was markedly lower than that of the shallow-growing Zostera marina.

ツノメガニ(スナガニ科)の日本海沿岸からの初記録

ツノメガニ(スナガニ科)の日本海沿岸からの初記録

The most continent-sided occurrence of the Phanerozoic subduction-related orogens in SW Japan: Zircon U-Pb dating of the Mizoguchi gneiss on the western foothill of Mt. Daisen volcano in Tottori

Understanding the pre-Cenozoic geotectonic framework along the Japan Sea coast in southwest Japan is critical in clarifying the relationship between oceanic subduction-related and collision-related geotectonic belts along the continental margin of East Asia. Although a thick Neogene-Quaternary volcanic-sedimentary cover often conceals the pre-Cenozoic units, the Western Honshu is one of the pivotal regions especially the Mizoguchi gneiss (high-grade gneisses up to amphibolite facies with Rb-Sr isochron age of 185Ma) exposed near Mt. Daisen in western Tottori prefecture. This unit, together with a neighboring 199Ma granitoid, was previously correlated with the Hida gneiss in Central Japan, located nearly 250km to the east. The present study examines this interpretation using zircon U-Pb geochronology. Ages of three gneissose rocks of the Mizoguchi gneiss reveals that the protolith is composed of and represented by granitoid, accretionary complex, and/or high pressure/low temperature (HP/LT) type metamorphosed units. In terms of protolith rock type and zircon age spectra, the Mizoguchi gneiss is different from the Hida gneiss that is interpreted to have been derived from sedimentary rocks/volcanics with continental shelf, and also from the Oki gneiss characterized by its preservation of abundant Precambrian detrital zircon grains. The high-grade metamorphism of the Mizoguchi gneiss is interpreted to have occurred after middle Jurassic as constrained by the youngest detrital grain. The protolith of the Mizoguchi gneiss belongs to the Suo belt (Jurassic HP/LT type metamorphosed accretionary complex) in southwest Japan; however, the unit is interpreted to have been metamorphosed by a Jurassic thermal event, which overlaps that of the Jurassic felsic magmatism in the Hida belt (the Funatsu episode). The Mizoguchi gneiss in western Honshu is unique, because it marks the northernmost or the most proximal occurrence of Phanerozoic subduction-accretion complex in Southwest Japan, clearly on the south of non-accretionary Oki and Hida belts.

Depth-varying azimuthal anisotropy in the Tohoku subduction channel

We determine a detailed 3-D model of azimuthal anisotropy tomography of the Tohoku subduction zone from the Japan Trench outer-rise to the back-arc near the Japan Sea coast, using a large number of high-quality P and S wave arrival-time data of local earthquakes recorded by the dense seismic network on the Japan Islands. Depth-varying seismic azimuthal anisotropy is revealed in the Tohoku subduction channel. The shallow portion of the Tohoku megathrust zone (<30 km depth) generally exhibits trench-normal fast-velocity directions (FVDs) except for the source area of the 2011 Tohoku-oki earthquake (Mw 9.0) where the FVD is nearly trench-parallel, whereas the deeper portion of the megathrust zone (at depths of ∼30–50 km) mainly exhibits trench-parallel FVDs. Trench-normal FVDs are revealed in the mantle wedge beneath the volcanic front and the back-arc. The Pacific plate mainly exhibits trench-parallel FVDs, except for the top portion of the subducting Pacific slab where visible trench-normal FVDs are revealed. A qualitative tectonic model is proposed to interpret such anisotropic features, suggesting transposition of earlier fabrics in the oceanic lithosphere into subduction-induced new structures in the subduction channel.