Time-lagged combined impact of the Pacific Decadal Oscillation on variations in the Tsugaru Warm Current, Japan Sea throughflow

Abstract Seismic research on the western (Sea of Japan) side of Japan is important for mitigating disasters caused by earthquakes and associated tsunamis because the plate boundary between the Okhotsk Plate and Amurian Plate is very close to the western coast of northern Japan. Here, we analyzed stress drops of 88 earthquakes (4.0 $$\le \text{M} \le$$ ≤ M ≤ 5.0) that occurred between 2003 and 2021 off the west coast of northern Japan to investigate their spatial pattern and its relationship with historical large earthquakes. Stress drops of the earthquakes ranged from 0.20 to 920 MPa and showed clear spatial heterogeneity. Stress drop values in the source area of the 1983 Central Sea of Japan earthquake were larger than those in the source area of the 1993 off the southwest coast of Hokkaido earthquake, consistent with previous studies on the source characteristics of the two earthquakes that had been estimated from Tsunami data. In addition, the region between the source areas of the two earthquakes showed the greatest stress drop values, suggesting that the high shear strength in that region prevented further rupture propagation during the two large earthquakes. Our results confirm that stress drops of small earthquakes provide important information on the frictional properties of plate boundaries. Graphical Abstract

Temperate seagrass meadows are foundation habitats, but their communities are hard to census. Here, I provide a first COI environmental DNA (eDNA) metabarcoding snapshot from seawater at a Zostera marina meadow in the Vostok Bay marine reserve (Peter the Great Bay, Sea of Japan). In September 2021, eDNA from two 900 mL replicates of water were filtered, isolated, amplified for the 313 bp COI fragment with dual-index PCR (multiple replicates), and sequenced on Illumina NovaSeq. I obtained 53,666 reads for 176 operational taxonomic units (OTUs). Eukaryota dominated (154 OTUs; 93.7% of reads), while 22 bacterial OTUs comprised 6.3%. The assemblage was largely photosynthetic microeukaryotes, especially diatoms (61 OTUs; 49% of reads), consistent with late-summer productivity. Metazoan detections included a strong signal of the phoronid Phoronopsis harmeri (7511 reads; 14%), diverse invertebrates, and few vertebrate reads (0.5%), indicating limited fish sensitivity of universal COI assays. One abundant OTU was initially assigned to the giant kelp Macrocystis pyrifera but was rejected after additional BLAST and phylogenetic checks, illustrating database-driven misassignments. COI eDNA offers rapid, low-impact screening for marine protected area monitoring, but robust use requires seasonal replication, multi-marker assays, and a curated regional reference library.

Kudoa septempunctata, a parasite found in olive flounder, poses a growing food safety risk in East Asia, particularly in Japan and South Korea. K. septempunctata poisoning caused by raw fish consumption causes brief gastrointestinal symptoms. However, long-term, national-scale aggregated epidemiological data for K. septempunctata food poisoning are limited. In this retrospective study, we examined the recent epidemiological trends and characteristics of K. septempunctata food poisoning cases reported in Japan between January 2013 and December 2023. Ministry of Health "Foodborne Illness Statistical Data" were assessed for case counts, outbreaks, and implicated foods. Reported cases totaled 2009, reaching a peak in 2014 (429 cases) then declining to < 100 cases during the COVID-19 pandemic. October had the highest number of monthly reports. Flounder, particularly sashimi and sushi, were implicated in 99% of cases. The highest case counts occurred in Yamaguchi, Osaka, and Fukuoka prefectures (160, 155, and 154, respectively). Tottori, Shimane, Yamaguchi and Oita prefectures had the highest incidence rates (14.3, 10.9, 10.7, and 10.7 per 1,000,000 population, respectively). Prefectures along the Sea of Japan typically reported higher incidence rates. This study highlights the importance of continued surveillance and reporting of K. septempunctata poisoning, and the need to consider Kudoa infections in the differential diagnosis of food poisoning cases involving raw fish consumption.

ABSTRACT Ray tracing of tsunamis generated at the Sea of Japan (SOJ) was performed to investigate far-field tsunami propagation in a semi-enclosed sea with complicated bottom features. This study focused on analyzing the propagation of the tsunami generated by the 2024 Noto Peninsula Earthquake that emerged in the southern SOJ, which differed from previously recorded large tsunami events that originated in the northern part of the SOJ. The tsunami propagation path and traveling time were estimated by predicting the wave refraction according to Snell’s Law. The numerical runs were made under the setting of four major tsunami events that occurred in the SOJ, and the calculated arrival time of the initial wave at the coast agreed well with the observed values. The trajectories of tsunami waves in the SOJ depend greatly on the meridional position of the wave source. In the case of the Noto Earthquake, the tsunami generated at the western and eastern parts of the rupture zone behaved differently, mainly due to the presence of the deep Toyama Submarine Canyon situated on the eastern side of the tsunami source. The findings of this study may aid in interpreting the observed or simulated results regarding tsunami propagation in the SOJ.

ABSTRACT Field surveys of tsunami heights caused by the January 1, 2024, Noto Peninsula earthquake (M 7.6, Japan Meteorological Agency) were conducted along approximately 700 km of coast from Yamagata Prefecture to Shimane Prefecture and on Sado Island, Japan. The region around the source area, which was severely damaged, was excluded. We measured tsunami heights of about 2–3 m at sites that were relatively close to the wave source area. The tsunami heights tended to be smaller or attenuated to an indistinguishable level at measurement points further away from the source area; however, a 1.4-m tsunami, which was higher than the tsunami heights in the surrounding areas, was found to have hit the port of Hyogo Prefecture, approximately 300 km from the wave source. To determine the overall magnitude of this tsunami, we estimated the tsunami magnitude m to be 1.5 from our measurement data and other published data. According to the relationship between the earthquake magnitude M and tsunami magnitude m of past earthquakes on the eastern margin of the Japan Sea, the m value of the 2024 tsunami was smaller than the value that would be expected from the earthquake magnitude.

Marine heatwaves (MHWs), discrete and prolonged periods of anomalously high ocean temperatures, have been occurring with increasing frequency and intensity in recent years, threatening global fisheries. This study employs nighttime imageries and random forest models to analyze the impacts of MHWs on Japanese flying squid (Todarodes pacificus) nighttime fisheries in the Sea of Japan (East Sea) (2014–2023). For the first time, critical MHWs thresholds were identified: monthly duration exceeding 16 days and cumulative intensity surpassing 50 °C·days trigger significant contraction of core fishing grounds, particularly in summer/autumn, exhibiting strong negative correlations to catch and vessel numbers (|r| > 0.7, p < 0.05). Sea surface temperature (SST) is the primary driver of spatiotemporal patterns of squid fishing grounds (45% model contribution), with optimal fishing conditions at 17.08 °C. Regional MHWs sensitivity varies across exclusive economic zones (EEZs), with the South Korean EEZ responding strongest (R² = 0.77) to MHWs characteristics. This research establishes novel MHWs impact thresholds for migratory squid fisheries and provides a data-driven framework for adaptive management in semi-enclosed seas, highlighting the urgency of addressing extreme climate events in fisheries governance.

Distribution and Size Composition of Whip Sculpin Gymnocanthus intermedius (Cottidae) in the Waters of Primorye (Sea of Japan) in Summer

Alternate rotating layered circulation in response to extrinsic and intrinsic forcing in the Japan sea

Variations in the 129I/127I ratios of pre-world war II algae under long-term exposure to atmospheric iodine isotopes.

Late Holocene hydroclimatic anomalies in the NW Japan Sea: Distinguishing moisture sources and Pacific linkages

Anaerobic oxidation of methane-associated carbon, nitrogen, and sulfur isotopic signatures in sediments of methane hydrate-bearing areas in northeastern Japan Sea.

The paper reveals pollen and spore findings from the Sea of Japan’s bottom sediments, namely the Tartary Trough, continental slope of Primorye, Russian Far East, as well as Northern Yamato and Pervenets rises in 2010. The Tartary Trough sediments contain a high percentage of pine, birch, and spruce pollen. Dominance of coniferous (spruce and pine) pollen is associated with the wide-spread distribution of the species as well as ability of this pollen to be aerially dispersed for hundreds of kilometers. Coniferous pollen (pine, spruce, and fir amount to approximately 90 %) and oak pollen (up to 20 %) dominate in the Pervenets Rise sediments. Pine and oak pollen prevail in the Northern Yamato Ridge sediments. Oak pollen presence in marine sediments increases from north to south, consistent with its range in the Sea of Japan region. The obtained data are likely to contribute to interpreting pollen records of marine sediments and paleoreconstruction of environmental conditions and climate.

ABSTRACT During the late summer (July–August) of 2024, the Northeast China (NEC) suffered extreme precipitation and severe floods, with rainfall in southern NEC marking the highest recorded since 1985. Using the daily precipitation records from 245 national meteorological stations across the NEC, this study analyses the characteristics of the rainfall anomalies and the associated large‐scale circulation patterns in the late summer of 2024. Based on the generalised equilibrium feedback analysis (GEFA) method, we investigate the response of precipitation and atmospheric circulation anomalies to sea surface temperature (SST) anomalies across various oceanic basins. The results indicate that the NEC precipitation anomalies in the late summer of 2024 exhibit a remarkable response to both the first empirical orthogonal function (EOF) mode of the North Pacific SST (NP1) and the second EOF mode of the tropical Atlantic SST (TA2). The NP1 features widespread positive SST anomalies extending from the Kuroshio Extension to the west coast of North America, and the TA2 is marked by positive anomalies in the northern tropical Atlantic and negative anomalies in the southeastern region. Both modes induce enhanced precipitation over NEC, with anomaly centres located southward, closely matching the observations. Specifically, the positive SST anomalies of the NP1 mode enhance the upward heat flux over the Japan Sea and its eastern regions, inducing positive geopotential height anomalies over Japan, thereby leading to an enhanced and northward anticyclone in the Northwest Pacific. Moreover, for the TA2 mode, the positive SST anomalies in the northern tropical Atlantic are closely associated with the downstream propagating Rossby wave train, resulting in an anomalous circulation pattern characterised by active Northeast China cold vortexes over the NEC and an intensified western Pacific subtropical high. These circulation anomalies facilitate the northward transport of warm and humid airflows to the NEC and promote the frequent convergence of cold and warm airflows over the NEC region, thereby contributing to the anomalously more precipitation over the NEC in the late summer of 2024. By quantifying the relative contributions of different SST modes, this study helps better target key precursors of NEC summer rainfall anomalies, which provides useful guidance for seasonal climate forecasting in NEC.

Abstract We compared the diet of larval Japanese sardine Sardinops melanostictus between the western and eastern areas of the Japanese coastal waters of the Sea of Japan in March–May 2019–2022. Standard lengths of larvae examined for gut contents ranged from 5 to 17 mm; in both areas, the main prey items found in the gut were copepod nauplii and copepodites. However, food incidence was low in eastern areas, and mean prey width differed between the areas. Larvae in the western area in March and April fed on copepods as large as the largest in ambient waters, such as the copepodites of Paracalanus spp. and the nauplii of large Calanoida, whereas the main food for larvae in the eastern area in May was small copepod nauplii such as those of Oithona spp. These differences suggest that the prey environment in the western area in March and April is more favorable for sardine larvae than in the eastern area in May. Understanding such spatial patterns in prey availability and larval diets would be essential for elucidating the survival and recruitment processes of Japanese sardine in the Sea of Japan.

ABSTRACT Pacific bluefin tuna ( Thunnus orientalis , PBF) are highly migratory, with a single Pacific‐wide stock facing complex management challenges due to extensive transoceanic movements and a recent population recovery. This study addresses persistent knowledge gaps regarding the quantitative contributions of different natal origins to key feeding grounds and the proportions of trans‐Pacific migrants in spawning grounds. We used stable isotope analysis of otoliths (δ 18 O oto and δ 13 C oto ) to investigate natal origins and migratory patterns of PBF collected from three key locations: the Philippine Sea–East China Sea (PS‐ECS), the Sea of Japan (SoJ), and the California Current Large Marine Ecosystem (CCLME). Our analysis of δ 18 O oto values effectively discriminated natal origins, revealing a strong dominance of PS‐ECS‐origin fish in catches across all areas. Specifically, 91% of PBF captured in the CCLME originated from the PS‐ECS spawning grounds, a proportion that surpassed estimates from those captured in SoJ and PS‐ECS. Additionally, the δ 13 C oto analysis successfully distinguished between trans‐Pacific migrants and resident individuals, confirming that a substantial proportion (87%) of adult PBF caught in the PS‐ECS spawning grounds have previously migrated to the CCLME. These results confirm the high connectivity of PBF across the Pacific and support its management as a single stock. The high proportion of PS‐ECS‐origin fish utilizing the CCLME as a critical feeding ground underscores the necessity of managing juvenile exploitation in Eastern Pacific waters to ensure sufficient survivorship and maximize the reproductive output of the adult spawning stock in the Western Pacific. The quantitative estimates of natal origins and migratory patterns derived from this study provide crucial data for future stock assessments and the development of improved spatially explicit management models.

BackgroundKudoa septempunctata, a parasite found in olive flounder, poses a growing food safety risk in East Asia, particularly Japan and South Korea. Linked to raw fish consumption, K. septempunctata poisoning causes brief gastrointestinal symptoms. This study aimed to characterize recent epidemiological trends and characteristics of K. septempunctata food poisoning by using national data from Japan.MethodsThis retrospective study examined Kudoa food poisoning cases reported in Japan between January 2013 and December 2023. Data from the Ministry of Health’s “Foodborne Illness Statistical Data” report were assessed for case counts, outbreaks, and implicated foods.ResultsA total of 2,009 cases were reported, peaking in 2014 (429 cases) and declining to < 100 cases since 2020. October had the highest number of monthly reports. The age distribution showed that the majority of cases occurred among older adults, with individuals aged 60–69 years (23.5%) and those 70 years and older (26.0%) together accounting for nearly half of all cases. Cases among individuals younger than 20 years comprised less than 2.5% of all cases. Flounder, particularly sashimi and sushi, were implicated in 99% of cases. The highest case counts occurred in Yamaguchi, Osaka, and Fukuoka prefectures (160, 155, and 154, respectively). Tottori, Shimane, Yamaguchi and Oita prefectures had the highest incidence rates (14.3, 10.9, 10.7, and 10.7 per 1,000,000 population, respectively). Prefectures along the Sea of Japan tended to report higher incidence rates.Conclusionhis is the first study to describe Kudoa food poisoning in Japan. Clinicians should consider Kudoa infections in cases of food poisoning involving raw fish.DisclosuresAll Authors: No reported disclosures

Reliability of the fish stock assessments is affected by many factors, including seasonal patterns of fish distribution and inhomogeneity of distribution density. Results of two bottom trawl surveys are compared, which were conducted in the same area of Peter the Great Bay (Japan Sea) and in the same year 2013 but in different seasons, as spring and summer. The fish species stock assessments were mostly higher in summer, with exclusion of sculpins with insignificant difference between the seasons (except actively migrated graypurple sculpin). The observed difference was reasoned by seasonal bathymetric migrations. Therefore, an optimal for trawl surveys season can be determined taking into account the bathymetric migration of bottom species. In spring, the fish concentrated mainly at the depths more than 300 m, with the maximum density of 24.86 t/km² in the range of 400–500 m, where walleye pollock and blackfin flounder prevailed. In summer, the highest concentration was found in the range of 20–50 m but its value was much lower, 14.5 t/km². No more than 10 % of fish biomass remained in the deep-water areas with the depth from 200 to 700 m. The fish concentration in dense but small-sized aggregations increases inhomogeneity of the biomass mosaic distribution and reduces accuracy of their stock assessments. That’s why the summer season with relatively even distribution of bottom fish is the optimal time for bottom trawl surveys.

In the first decade of 21st century, aggregations of japanese anchovy were regularly observed off the western and eastern coasts of Sakhalin in summer and autumn seasons, where reached 52о00′ N in the Tatar Strait and 53о20′ N in the Okhotsk Sea. In total, they migrated to the eastern coast during 23 years and to the western coast during 35 years (since 1989 till 2023). The anchovy approaches to the Sakhalin coasts corresponded with dynamics of this species populations in the Tsushima Current and Kuroshio waters and coincided well with the period of japanese sardine depression both in the Japan Sea and North-West Pacific. In the years of high abundance, about 100–300 thousand tons of japanese anchovy could be landed at Sakhalin annually, if the fishery would be organized properly.

Diurnal variation analysis of fluorescence quantum yield during algal blooms based on geostationary ocean color satellite.