Wind-induced coastal upwelling plays a significant role in ocean circulations and ecosystems. Although coastal upwelling along eastern boundaries by trade winds is well known, coastal upwelling along western boundaries and its effects in the North-East Pacific Ocean have not been well investigated in previous studies. This study presents surface nutrient supply owing to coastal upwelling along the southeast coast of the Japanese mainland in summer investigated with a coupled physical-biogeochemical model. The model is validated against satellite-based observations (surface temperature and chlorophyll-a), showing good agreement between the model and observations. The summer monsoon (southerly wind) induces coastal upwelling along the coast, leading to rich nutrient conditions near the surface and phytoplankton blooms in the study area. The model results show two hotspots of coastal upwelling on the east sides of the Kii and Boso Peninsulas. Although vertical current transport and turbulent diffusion contribute equally to the surface nitrate supply along the peninsulas, coastal upwelling is identified as the primary contributor to variations in the nutrient supply. In addition to the direct advective surface nutrient supply, coastal upwelling strengthens the vertical nutrient gradient, thereby enhancing vertical diffusive nutrient transport. The Kuroshio Current passes near the upwelling regions, resulting in highly concentrated nutrient/phytoplankton water uptake to the sea surface downstream of the Kuroshio, which results in the nutrient/phytoplankton stream.

Wave-driven channel flows in coral reefs have been described, but their interpretation within a rip current framework has remained less developed than for sandy shores. Here, a rip current in a fringing coral reef was investigated through field observations and an idealized numerical model. Velocity profiles and wave conditions were measured within the reef channel and at an offshore site to characterize incident wave forcing. An idealized numerical model, validated against observations, was used to examine the momentum balance and quantify offshore transport associated with the reef-gap rip current. Field observations revealed that 73% of the variance in offshore-directed flow velocity can be explained by incoming significant wave height, compared with 7.7% for tidal currents. Similar to rip currents on sandy shores, the rip current at this fringing reef site was forced by incoming wave energy and modulated by tidal elevation. The modeled cross-shore momentum balance within the channel suggested that the main driving forces were pressure gradients, nonlinear advection, and wave-breaking dissipation, while bottom friction played only a secondary role in the channel. Offshore export increased with incident wave height under low to moderate wave conditions but saturated under high waves, possibly reflecting a shift in the partitioning between the mean and transient eddy motions. The integrated observational and modeling approach advances understanding of reef channel circulation within the rip current framework and clarifies both shared dynamics and distinctive features of offshore transport in coral reef environments.

We developed a Transformer-based method for positron track reconstruction in the MEG II experiment. The model acts as a hit classifier to remove pileup hits in the MEG II drift chamber, which operates under a high pileup occupancy of 35-50 %. The trained model significantly improved hit purity, leading to enhancements in tracking efficiency and resolution by 15 % and 5 %, respectively, at a muon stopping rate of 5 & times; 107 & micro;/sec. This improvement translates into an approximately 10 % increase in the sensitivity of the & micro;- ey branching ratio measurement.

Towards the desirable preservation of the marine environment under a changing global climate, this study aims to investigate the coastal biological response to varying oceanic conditions, namely the Kuroshio meander, and associated nitrate transport on the Pacific coast of Japan around the Enshu-nada Sea, using a coupled three-dimensional regional ocean circulation model with a nitrogen-based ecosystem model. A prominent difference was found in nitrate transport processes between for a period when the Kuroshio took a meandering path and for a non-meandering period, leading to about 1.5 times higher surface primary production measured by chlorophyl-a concentration during the non-meandering period than during the meandering period. The upper ocean nitrate flux budget analysis showed that the subsurface nitrate was transported upward as a vertical diffusive flux around the north (shoreward) of the Kuroshio path and as a mean vertical advective flux in the Kuroshio downstream region around the Izu-Ogasawara Ridge. In contrast, high-frequency eddy vertical advective fluxes caused downward transport, but to a degree about 20% smaller than the other fluxes. After nitrate was supplied to the upper layer, it was transported horizontally by the counterclockwise rotating cyclonic eddy formed between the coast and the Kuroshio and supplied to phytoplankton in the Enshu-nada Sea. These results suggest that carbon sequestration due to biological pump may also vary in response to the Kuroshio that is influenced by basin-scale oceanic conditions.

Searches for charged lepton flavor violation in the muon sector stand out among the most sensitive and clean probes for physics beyond the Standard Model. Currently, μ^+ →e^+ γ experiments provide the best constraints in this field for a wide range of models while, in the coming years, new experiments investigating the processes of μ^+ →e^+ e^+ e^- and μ→e conversion in the nuclear field are anticipated to reach comparable or higher sensitivities. The High-Intensity Muon Beam (HIMB) facility at PSI, which is expected to deliver muon beam intensities up to two orders of magnitude higher than the existing beam lines, offers a unique opportunity to significantly enhance the sensitivity of μ^+ →e^+ γ searches. The discovery potential could be substantially boosted and a sensitivity comparable to that of all the other projects could be reestablished, which is essential for discriminating among competing new-physics scenarios should an observation occur in any of the channels. In this document, we express our interest in developing a μ^+ →e^+ γ experimental program at HIMB, with the goal of improving, within the next decade, the sensitivity of the μ^+ →e^+ γ search by more than one order of magnitude relative to the expected final result of the current leading experiment, MEG II. This effort would ensure that PSI retains its leadership in this field.

The Seto Inland Sea (SIS) harbors abundant aquatic biological diversity, while its ecosystem has been affected by climate change in recent years. Previous studies have shown that the residual current in the SIS varies significantly under the influence of the Kuroshio. To isolate the open ocean influences, salinity transport and the associated salinity budget in the SIS were investigated, as a conservative variable characterizing the estuarine hydrodynamics, using a high-resolution, long-term 3D circulation model. Our findings indicate that the fluctuations of salinity fluxes were influenced by the position of the Kuroshio axis and were highly correlated with the associated volume fluxes. The clockwise eastward transport from Bungo to Kii varies seasonally with an increase in winter and a decrease or counterclockwise increase in summer. The total salinity in each of the eight sub-basins of the SIS was also correlated with the salinity fluxes at the straits connecting the sub-basins. The total salinity in the western sub-basins increased with the eastward clockwise transport and decreased with the westward counterclockwise transport, whereas the eastern sub-basins showed less correlations, resulting in a zonal difference of salinity response to the open ocean.

Quantifying seed dispersal and connectivity are crucial for effective conservation of the declining eelgrass, Zostera marina. The Seto Inland Sea (SIS), Japan, is a prototypical basin-strait system, a type of marine environment ubiquitous worldwide. The unique geography and hydrodynamic conditions of the SIS exert a profound influence on the connectivity of eelgrass populations via ocean currents. This study assessed connectivity by tracking the rafting of seeds among eelgrass populations in the SIS, using a regional oceanic circulation model coupled with a Lagrangian particle tracking model. The coupled model demonstrated that the interaction between the topographically constrained tidal residual currents and density-driven geostrophic circulation created a physical barrier to seed dispersal in the strait and promoted basin-scale connectivity. The restricted connectivity between the two sides of the SIS is also supported by the genetic structure of the eelgrass populations. Our findings provide a better understanding of the ecological connectivity in marine organisms that are spread by rafting in other basin-strait systems with analogous oceanic conditions, as well as in eelgrass populations.

Gene flow is a crucial concept in the delineation of conservation units for natural populations of a species. Seagrasses are marine species targeted for conservation because their abundance has declined worldwide during the last century. However, knowledge of how to delineate seagrass conservation units based on their genetic structure is inadequate. In this study, the genomes of Zostera marina L. (eelgrass) populations in three semi-enclosed areas with different spatial scales in Japan were analyzed using single nucleotide polymorphisms within genome-wide loci, and their genetic structures were explored in the context of their isolation caused by geographical distance and barriers. Isolation by distance was apparent at spatial scales of 200–2000 km. A barrier apparently due to a narrow strait in an area with linear dimensions less than 200 km led to greater genetic isolation than did distance. On a more local scale, we found that heterogeneity among sites and intra-site variability rather than isolation by distance or barriers governed the genetic structure of eelgrass on spatial scales less than 20 km. Our results imply that future seagrass conservation efforts should make more use than before of genomic tools so that greater attention can be focused on the complex structures formed on local scales. Identifying the ecological importance of genetic heterogeneity and the functional meaning of genetic differences on local scales will be among the next challenges to the delineation of seagrass conservation units.

In recent years, global warming has intensified coral bleaching worldwide. The mesophotic zone (MPZ) at depths of 30-150 meters, where photosynthesis is viable and water temperatures are stable, is expected to serve as a refuge and gene resupply source for shallow-water corals. This study quantitatively evaluates the 3D population connectivity between shallow-water corals and MPZ corals in the potential coral habitats surrounding Okinawa Island. Utilizing a triple-nested high-resolution 3D ocean circulation model, an offline, 3D Lagrangian advection-dispersion model for planktonic coral larvae was developed. Results show that 3D intra-island coral connectivity is strongly influenced by topographically constrained residual currents around the island. Coral larvae released from shallow areas are transported in a clockwise direction around the island. While the larvae released from the west coast are transported to the east coast by crossing the northern tip of the island, their movement is significantly hindered at the southern tip by a shallow channel as a topographic barrier. Conversely, this clockwise transport is much less pronounced in the MPZ, resulting in lower connectivity between the west and east coasts. In addition, potential source areas of coral larvae were analyzed to determine an island-wide coral network that could support coral conservation efforts in Okinawa.

This study presents remotely generated internal tides that propagate into shallow regions and are modulated by background flows using numerical simulations and field observation data. Numerical results indicate that strongly enhanced semi-diurnal (similar to M2) internal tide energy is generated over a shallow ridge, the Izu-Ogasawara Ridge. The generated internal tides propagates toward the Kuroshio upstream and shoal toward shallow regions near Cape Shiono-Misaki. The intensified internal tide energy flux toward the cape is explained by two mechanisms: (a) intensified internal tide generation over the ridge due to the interaction between tides and the Kuroshio and (b) wave energy convergence along the Kuroshio due to wave refractions. A 13-year field data set obtained from the cape was used to investigate shoaling internal tides influenced by the Kuroshio. The observed results reveal a significant positive correlation between the kinetic energy of semi-diurnal internal tides and the background flows caused by the Kuroshio, which evidently supports the intensified internal tides attributed to the interaction between background flows and tides, as proposed by recent studies. The intensity of shoaling internal tides is also largely influenced by the path of the Kuroshio and seasonal effects. The magnitude of shoaling internal tides is clearly weaken as the Kuroshio meander occurs. Shoaling internal tides modulated by the Kuroshio can provide new insights into energy transport and mixing processes in coastal oceans. Oceans worldwide have internal waves that significantly contribute to the transport of mass and heat within the oceans. In particular, internal waves propagating into shallow coastal regions result in enhanced energy dissipation accompanied by strong mixing and transport, similar to ocean surface waves. Internal waves at tidal frequencies are called internal tides and energetically dominate other internal waves in coastal regions. However, difficulties in observing the physical processes associated with internal tides have hindered the comprehensive elucidation of internal tides. This study presents shoaling internal tides generated by the combined effects of the Kuroshio and tides over a shallow ridge using numerical simulations and field observations. The numerical results show clear processes of shoaling internal tides propagating toward the Cape, generated by the interaction between the Kuroshio and the tides. Long-term (13-year) field observation data obtained from the Cape show that the magnitude of internal tides is significantly intensified by the magnitude of the Kuroshio, clearly indicating that the Kuroshio path/meander modulates shoaling internal tides. The shoaling internal tides observed in this study are anticipated to contribute to mixing and transport in coastal oceans. Shoaling internal tide are investigated with a numerical model and a long-term field data set The Kuroshio intensifies generation of internal tides over a shallow ridge resulting in shoaling internal tides The Kuroshio meander greatly influences the magnitude of shoaling internal tides

Gene flow is a crucial concept in the delineation of conservation units for natural populations of a species. Seagrasses are marine species targeted for conservation because their abundance has declined worldwide during the last century. However, we cannot determine how to delineate conservation units with inadequate knowledge of the genetic structure of seagrasses. This study explored the genetic structure of Zostera marina L. (eelgrass) populations in three semi-enclosed areas using single nucleotide polymorphisms within abundant, genome-wide loci. Genome-wide markers revealed that the genetic structure was isolated by geographical distance and barriers through a narrow strait in an area with linear dimensions less than 200 km. The genetic distance created by the barrier was 6.7 times the genetic distance due to 100 km of geographic distance. The markers revealed the intra-site variability in genetic structure and the heterogeneity among sites on scales less than ~10 km that had not been recognized previously. Our results imply that the use of genomic tools will focus seagrass conservation efforts more locally than before and that assessing relative genetic differences can make delineating conservation units a reality. Identifying the evolutionary and quantitative meaning of genetic differences will be a next challenge for delineating seagrass conservation units.