Search

On-top hydrogen on a Pd cathode (Pd–H) was observed for the first time by operando infrared (IR) spectroscopy at 2030 cm−1, being stabilized by co-adsorbed solvent (n-alkane) molecules. A proton-exchange membrane (PEM) reactor with Pt/C (anode) and Pd/C (cathode) catalysts was modified to transmit an infrared (IR) beam for operando observation. Pd–H species was observed when 1) H+ was supplied to the cathodic chamber through the PEM, 2) solvent was flowed at the cathode, and 3) an appropriate bias was applied to the cathode. Because atomic H on Pd surfaces interacts with multiple Pd atoms, on-top Pd–H is proposed to be stabilized by co-adsorbed solvent molecules. Spectra of the solvent were deformed when Pd–H species were present: the peak intensity increased and nonfundamental bands at 2800–2500 cm−1 became pronounced. The intensification of these bands was caused by resonance with free-electron absorption bands in the IR region.

Updating predicting models could greatly improve the hit rate of virtual screening for identifying Keap1/Nrf2 protein–protein interaction inhibitors.

We report the diastereoselective electrocatalytic hydrogenation of cyclic ketones using a proton-exchange membrane (PEM) reactor. Adsorbed monoatomic hydrogen species (Hads) generated from protons at the triple-phase boundary of the cathode were found to reduce the C=O bond of cyclic ketones with high diastereoselectivity; cis-selectivity as high as 94% was achieved under the optimal conditions using a Rh catalyst. Operando infrared (IR) spectroscopy enabled the direct observation of adsorbed ketones involved in the reaction. We also demonstrated the 5 g-scale electrolysis of 4-tert-butylcyclohexanone by combining the hydrogenation process with water oxidation as an anodic reaction. This reaction successfully produced cis-4-tert-butylcyclohexanol, which is 52 times more expensive than the starting material based on commercial prices, using only electric energy and water as reagents and, importantly, without H2 gas. This research demonstrates the potential of PEM reactors as reliable, robust, and green systems for the electrochemical production of fine chemicals.

The Izu Ridge off the southern coast of Japan is composed of many seamounts and knolls and is an important fishery ground and hatchery for commercially important fish. As pelagic copepods link lower and higher trophic levels, we investigated the epipelagic copepods in the Izu Ridge using 28S DNA/RNA metabarcoding and microscopic approaches. In comparison with off-ridge regions, a low water temperature and high chlorophyll a concentration were observed in the Izu Ridge, possibly attributed to high levels of nutrients supplied by strong turbulences around the complex topography. We observed unique copepod communities with a large total biomass in the Izu Ridge, owing to the increased dominance of large copepod species. rRNA:rDNA (28S ratio) of these large species mainly showed positive correlations with the chlorophyll a concentration, suggesting a rapid response to the food supply. Migrating copepods were less dominant around the Izu Ridge with a shallow water depth. Higher species diversity and more rare species were detected in the Izu Ridge, which might be maintained by complex environment conditions including temporal and spatial variations in the concentration of chlorophyll a. Thus, the combined approach characterized copepod community structure and diversity supporting the rich pelagic ecosystems in the Izu Ridge.

Small copepods are important prey for fish larvae in the Kuroshio region off southern Japan. However, revealing entire community structures of small copepods is difficult using conventional methods. We applied a metabarcoding method to size-fractionated community samples of epipelagic copepods (small: 0.1-0.5 mm, medium: 0.5-1.0 mm, and large: 1.0-2.0 mm). Samples were collected from 2013 to 2016 from the shoreward (Kuroshio Slope, KS) and oceanic (Kuroshio Gyre, KG) sides of the Kuroshio Current at 138° E; the results were compared with those in the center of the subtropical gyre (SG). The KS and KG sites showed both spatial differences and seasonal changes, with distinct differences between winter-spring and summer-autumn in each size-fractionated community. Water temperature markedly influenced copepod diversity and community structure, especially in the small size fraction. Warm-water species in the SG intruded into the Kuroshio regions during high-temperature periods, leading to high diversity in summer-autumn. Inter-annual environmental variations influenced by temperature and productivity were evident in KS, leading to clear changes in the sequence proportions of dominant small copepods includingParacalanussp. and immature stages of the large copepodCalanus sinicus. Immature stages of medium/large copepods formed a substantial proportion of small-copepod communities in the Kuroshio regions (KS: 28.8%; KG: 24.7%; SG: 11.9%; based on average proportions of sequence reads). Because of their ecological importance and sensitivity to environmental changes, monitoring communities of small copepods with high taxonomic resolution may provide further insights into marine ecosystems, including fish recruitment, in the Kuroshio region.

The highly efficient chemoselective electrocatalytic hydrogenation of benzoic acids (BAs) to cyclohexanecarboxylic acids (CCAs) was carried out in a proton-exchange membrane reactor under mild conditions without hydrogenation of the carboxyl group. Among the investigated catalysts, the PtRu alloy catalyst was found to be the most suitable for achieving high current efficiencies for production of CCAs. An electrochemical spillover mechanism on the PtRu alloy catalyst was also proposed.

Japanese comics (called manga) are traditionally created in monochrome format. In recent years, in addition to monochrome comics, full color comics, a more attractive medium, have appeared. Unfortunately, color comics require manual colorization, which incurs high labor costs. Although automatic colorization methods have been recently proposed, most of them are designed for illustrations, not for comics. Unlike illustrations, since comics are composed of many consecutive images, the painting style must be consistent. To realize consistent colorization, we propose here a semi-automatic colorization method based on generative adversarial networks (GAN); the method learns the painting style of a specific comic from small amount of training data. The proposed method takes a pair of a screen tone image and a flat colored image as input, and outputs a colorized image. Experiments show that the proposed method achieves better performance than the existing alternatives., Comment: Accepted to ICIP 2021

Protein–protein interactions (PPIs) are prospective but challenging targets for drug discovery, because screening using traditional small-molecule libraries often fails to identify hits. Recently, we developed a PPI-oriented library comprising 12,593 small-to-medium-sized newly synthesized molecules. This study validates a promising combined method using PPI-oriented library and ligand-based virtual screening (LBVS) to discover novel PPI inhibitory compounds for Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2). We performed LBVS with two random forest models against our PPI library and the following time-resolved fluorescence resonance energy transfer (TR-FRET) assays of 620 compounds identified 15 specific hit compounds. The high hit rates for the entire PPI library (estimated 0.56–1.3%) and the LBVS (maximum 5.4%) compared to a conventional screening library showed the utility of the library and the efficiency of LBVS. All the hit compounds possessed novel structures with Tanimoto similarity ≤ 0.26 to known Keap1/Nrf2 inhibitors and aqueous solubility (AlogP

Cyclic alcohols are important building blocks of pharmaceuticals, perfumes, and liquid crystals. For instance, 4-tert-butylcyclohexyl acetate, which is derived from 4-tert-butylcyclohexanol (1), is a commercialized synthetic fragrance that is used more than 106 kg per year. The fragrance of its cis-isomer is more potent odorant than that of its trans-isomer, and hence, cis-4-tert-butylcyclohexyl acetate is obtained by acetylation of the corresponding alcohol, i.e., cis-1. On the other hand, cis-1 is generally obtained by the reduction of 4-tert-butylcyclohexanone (2). The use of sterically hindered L-selectride as a reductant gave 1 with 93% cis-isomer selectivity [1]. The stereoselective hydrogenation of ketone 2 to 1 with ruthenium-aminophosphine complexes using hydrogen gas and base also afford 96% cis-isomer [2]. Although high cis-selectivity is achieved by these methods, the use of hazardous reagents and their separation problems in the workup humper the large-scale application. Replacement of such homogeneous reductions (hydrogenations) by heterogeneous catalytic systems brings several economic and technical advantages. A major advantage of using heterogeneous catalysts is that the catalyst can be recovered from the reaction mixture by simple filtration. Therefore, the highly diastereoselective reduction (hydrogenation) of cyclic ketones using heterogeneous catalysts is a meaningful and challenging topic for sustainable chemistry. Here, we demonstrate the electrocatalytic hydrogenation of mono-substituted cyclohexanones in a proton exchange membrane (PEM) reactor (Figure 1a). We have investigated the effect of catalyst materials and current density on the current efficiency and cis-selectivity of the desired products. As a result, it was found that the use of the PEM reactor with Rh catalyst gave 1 with high cis-selectivity (94%) and high current efficiency (93%), as shown in Figures 1b and c. In addition, it was also confirmed that the present system was capable of continuous operation for several tens of hours and gram-scale electrolysis without loss of diastereoselectivity. Unlike conventional hydrogenation methods that are carried out under high temperature and high pressure, the PEM reactor can carry out the desired hydrogenation reaction under ambient temperature and pressure, which also suggests a significant improvement in energy efficiency. Furthermore, the reaction products are easily separated and the catalyst is highly recyclable. Thus, the hydrogenation using PEM reactors can realize energy-saving and clean organic reaction processes. The authors gratefully acknowledged support by JST CREST Grant No. JPMJCR18R1, Japan. References [1] Brown, H.C.; Krishnamurthy, S.J. Lithium Tri-sec-butylborohydride. New Reagent for the Reduction of Cyclic and Bicyclic Ketones with Super Stereoselectivity. Remarkably Simple and Practical Procedure for the Conversion of Ketones to Alcohols in Exceptionally High Stereochemical Purity. J. Am. Chem. Soc. 1972, 94, 7159–7161. [2] Abdur-Rashid, K.; Chen, X.; Guo, R.; Jia, W. Method for the preparation of cis-4-tert-butylcyclohexanol. U.S. Patent 2010/0204524, A1, 2010. Figure 1

Metabarcoding technology using high-throughput sequencing has revolutionized the current understanding of the diversity and ecology of eukaryotic microorganisms. The aim of the present study was to investigate vertical and seasonal variation in eukaryotic plankton communities and to assess the diversity of eukaryotic plankton, using 18S rRNA sequencing, over a depth gradient in subtropical waters affected by the Kuroshio Current. In particular, the present study focused on the diversity and ecology of Alveolata and Rhizaria taxa, which include a variety of plankton species with fragile skeletons or soft bodies. Three vertically distinct eukaryotic communities were identified: the Kuroshio-influenced epipelagic zone (

Floating plastic debris was investigated in the transition region in the North Pacific between 141°E and 165°W to understand its transportation process from Asian coast to central subtropical Pacific. Distribution was influenced primarily by the current system and the generation process of the high concentration area differed between the western and eastern areas. West of 180°, debris largely accumulated around nearshore convergent area and was transported by eddies and quasi-stationary jet from south to the subarctic region. The average was 15% higher than that previously reported in 1989, suggesting an increase in plastic debris in 30 years. East of 180°, debris concentrated in the calm water downstream of the Kuroshio Extension Bifurcation with considerably high concentration (505,032 ± 991,989 pieces km−2), due to the accumulation of small transparent film caused by calm weather conditions, suggesting a further investigation on small plastic (

Fibrous nanomaterials suspended in liquid form gel structures when the binding sites between the components reach sufficient number densities. Cellulose nanofibers (CNFs) are one of such nanomaterials, and transparent papers are fabricated by drying their aqueous dispersions. It is therefore important to characterize the wet state, but the specific fluorescent marker molecules are not available for arbitrary CNFs. We report an approach based on the single particle tracking of Brownian probe particles. We focus on the nonuniformity in the Brownian motion to detect the partial structural order between sol and gel, which is nontrivial to characterize. The simple logarithmic measure of diffusive behavior reveals the multimodal nature of Brownian motion depending on the CNF concentration. The subdiffusive behavior by the overall mean squared displacements alone does not tell whether it is caused by confinement in the local environment by CNFs, or binding to single CNFs possibly diffusing in the dispersion. However, the particle-size dependence clarifies that it is not caused by binding but the confinement effect. Furthermore, the logarithmic measure approach enables the detection of overlapping distributions through their heads rather than tails. The detection of partial structural order by rheological non-uniformity of the system with a simple approach will contribute to the further understanding of gel forming materials in general.

A continuous survey examined short-term variations in the zooplankton community and physical ocean environment from the northeastern Izu Islands to Boso Peninsula in Japan. High copepod abundance and small upwellings in the surface layer and salinity minimum layer in the subsurface were observed on the north side of coastal fronts in the westernmost transect, moving southward as the Kuroshio Current left the Boso Peninsula. Thus, the salinity minimum layer might be a key factor forming upwelling and the fronts, leading to large abundance of coastal copepods off the northeastern Izu Islands. A community structure analysis of calanoid copepods revealed an intermediate belt assemblage between coastal and offshore (Kuroshio) assemblages. Copepod abundance was remarkably low and Ctenocalanus vanus dominated (nearly 37%) in the intermediate belt zone, indicating that C. vanus has a relatively high tolerance to adverse environments for calanoid copepods. As the Kuroshio Current left the Boso Peninsula, the coastal assemblage expanded in the same direction, and the intermediate belt assemblage off the northeastern Izu Islands disappeared. The largest population of Calanus sinicus was found along the two western transects off the northeastern Izu Islands (>1000 m depth), which was assumed to be transported from Sagami Bay and advanced southwestward while growing from copepodite stages CIII to CV. Larvae of C. sinicus would be an important food for fish larvae in addition to Paracalanus parvus s.l., the numerically dominant species in the coastal assemblage, and C. vanus under the adverse conditions for coastal copepods.

Motivation Functional prediction of paralogs is challenging in bioinformatics because of rapid functional diversification after gene duplication events combined with parallel acquisitions of similar functions by different paralogs. Plant type III polyketide synthases (PKSs), producing various secondary metabolites, represent a paralogous family that has undergone gene duplication and functional alteration. Currently, there is no computational method available for the functional prediction of type III PKSs. Results We developed a plant type III PKS reaction predictor, pPAP, based on the recently proposed classification of type III PKSs. pPAP combines two kinds of similarity measures: one calculated by profile hidden Markov models (pHMMs) built from functionally and structurally important partial sequence regions, and the other based on mutual information between residue positions. pPAP targets PKSs acting on ring-type starter substrates, and classifies their functions into four reaction types. The pHMM approach discriminated two reaction types with high accuracy (97.5%, 39/40), but its accuracy decreased when discriminating three reaction types (87.8%, 43/49). When combined with a correlation-based approach, all 49 PKSs were correctly discriminated, and pPAP was still highly accurate (91.4%, 64/70) even after adding other reaction types. These results suggest pPAP, which is based on linear discriminant analyses of similarity measures, is effective for plant type III PKS function prediction. Availability and Implementation pPAP is freely available at ftp://ftp.genome.jp/pub/tools/ppap/ Supplementary information Supplementary data are available at Bioinformatics online.

To understand long-term mean and seasonal variations of the Oyashio transport off the southeastern coast of Hokkaido, time series of estimated transports were generated by combining satellite altimetry and CTD data from the period 1993–2014 along a monitoring transect referred to as the “A-line”. Linear regressions between CTD-derived geostrophic transport and altimetry-derived sea level anomaly differences were calculated by minimizing a cost function newly proposed in this study. The horizontal structure of 21-year mean transport was characterized by a southwestward flow on the continental slope (SW-1) associated with the First Oyashio Intrusion, a northeastward flow (NE-2) likely trapped against the Kuril-Kamchatka trench, a southwestward flow (SW-3) related to the Second Oyashio Intrusion, and a very stable northeastward flow (NE-4) corresponding to a combination of the Oyashio Return Flow and quasi-stationary Jet. Analysis of long-term mean monthly transports revealed four alternating flows that were present throughout all seasons of the year. The boundaries between adjacent pairs of the four flows on the A-line did not change on a seasonal timescale as much as the southernmost latitude of the First Oyashio Intrusion. At a 0-month (1-month) time lag, the sum of the SW-1, NE-2, and SW-3 (SW-1 and NE-2) transports, which corresponds to net Oyashio transport (partial net Oyashio transport related to the southernmost latitude of the First Oyashio Intrusion), was correlated with Sverdrup transport more robustly than was each of the four alternating flows. This result suggests that as the Oyashio crossed the A-line, it responded barotropically to basin-scale wind stress by adjusting transports composed of both southwestward and northeastward flows.

To address various fisheries science problems around Japan, the Japan Fisheries Research and Education Agency (FRA) has developed an ocean forecast system by combining an ocean circulation model based on the Regional Ocean Modeling System (ROMS) with three-dimensional variational analysis schemes. This system, which is called FRA-ROMS, is a basic and essential tool for the systematic conduct of fisheries science. The main aim of FRA-ROMS is to realistically simulate mesoscale variations over the Kuroshio-Oyashio region. Here, in situ oceanographic and satellite data were assimilated into FRA-ROMS using a weekly time window. We first examined the reproducibility through comparison with several oceanographic datasets with an Eulerian reference frame. FRA-ROMS was able to reproduce representative features of mesoscale variations such as the position of the Kuroshio path, variability of the Kuroshio Extension, and southward intrusions of the Oyashio. Second, using a Lagrangian reference frame, we estimated position errors between ocean drifters and particles passively transported by simulated currents, because particle tracking is an essential technique used in applications of reanalysis products to fisheries science. Finally, we summarize recent and ongoing fisheries studies that use FRA-ROMS and mention several new developments and enhancements that will be implemented in the near future.

Polyketide synthases (PKSs) catalyze the sequential condensation of simple acetate units to produce a large class of natural products, including pharmacologically valuable compounds. PKSs are classified into three types on the basis of their domain structures; type III PKSs have the simplest domain structure, although their products have various structures and functions. The sequence-function relationship is fundamental for predicting enzyme functions, but it has not been well investigated in type III PKSs to date. Consequently, the current methods for predicting type III PKS functions are still immature in comparison with those that target type I/II PKSs. In this review we summarize the current functional and phylogenomic knowledge about type III PKSs and propose a new classification of their enzymatic reactions. We also discuss possible directions for the development of better computational tools for functional prediction of type III PKS homologues.

Growth variability was examined for Pacific saury Cololabis saira larvae under contrasting environments across the Kuroshio axis, based on samples collected during the winter spawning season in 2013 and 2014. The growth rate index (residual of the otolith marginal 3-day mean increment width from the linear regression on knob length) of larvae was compared among three areas: the inshore side of the Kuroshio axis, the Kuroshio axis, and the offshore side of the Kuroshio axis in relation to sea surface temperature (SST), salinity (SSS) and chlorophyll-a (CHL) concentration. The larvae were more densely distributed in the Kuroshio axis and offshore areas of higher temperature and salinity and lower chlorophyll-a concentration than in the inshore areas of lower temperature and salinity and higher chlorophyll-a concentration. No marked differences in the growth rate index were found among the three areas, even though the larvae in the inshore areas showed slightly higher growth rates in 2013. Despite the broad ranges of environmental factors, no clear relationship between the growth rate index and any environmental factor was detected. The survival potential of Pacific saury larvae was considered to be at least comparable under contrasting environments across the Kuroshio axis. Such a geographical homogeneity is concluded to be attributable to compensable effects of physical and biological factors. We hypothesize that the minority under physically-unfavorable but biologically-favorable conditions on the inshore side of the Kuroshio axis could survive equally well as the majority under physically-favorable but biologically-unfavorable conditions around the Kuroshio axis and on the offshore side of the Kuroshio axis.

The Western Isoguchi Jet, a quasi-stationary baroclinic jet that separates from the Kuroshio Extension, has been detected for a decade. Here we report the first observations of the vertical structure and temporal variations of the jet via moored current meters (September 2011–September 2012) and intensive hydrographic measurements (September 2010, 2011, and 2012). The jet flows northeastward and supplies subtropical water (northeastward velocity was ∼ 0.16 m s−1 and temperature was ∼ 4.4 ° C at 300 m depth, and they were ∼ 0.05 m s−1 and ∼ 2.9 ° C at 1000 m depth). We newly estimated the volume, heat, and salt transports of the jet to be 13.6–26.5 Sv, 0.0745–0.173 PW (reference potential temperature of 4.0 ° C ), and 5.58–9.91 × 10 6 kg s−1 (reference salinity of 33.5), respectively. Year-to-year changes of the jet axis complicated its horizontal distribution. The jet flowed stably northeastward throughout the year with weak seasonal variability. The vertical structure of the jet is quite different from that of the surrounding flow. These observations are consistent with the mechanism proposed by Mitsudera et al. (2018) and Miyama et al. (2018) to be responsible for the formation and maintenance of the jet.

We investigated the interdecadal trend of Oyashio velocity and transport during 1993–2011 based mainly on linear trend analysis of altimetry and in situ temperature-salinity data from a monitoring line (“A-line”) off the southeastern Hokkaido coast. Significant trends of increasing sea level were detected on the continental slope, north of the Kuril-Kamchatka Trench. Sea level anomaly data revealed a localized clockwise circulation centered near the trench, the suggestion being that the strength of the Oyashio on the slope and the offshore return flow had decreased. The Oyashio mainstream seemed to have shifted from a nearshore to an offshore path. Steric heights estimated from the A-line data exhibited an increasing trend north of the trench, where 50–80% of the increase was determined by halosteric components attributable to a trend of decreasing salinity in the subsurface. The trend of decreasing salinity was related to downward displacement of isohaline/isopycnal surfaces. The largest displacement was above the trench. Horizontal pressure gradients associated with southwestward flows on the slope were weakened. The Oyashio transport decreased by 8.9 Sv (106 m3 s−1) in 19 years. A mesoscale eddy analysis revealed that clockwise eddies appeared more frequently in recent years near the trench around the A-line and could decrease the Oyashio transport. A baroclinic, long Rossby-wave model also predicted that a large-scale baroclinic response to the wind stress could weaken the Oyashio velocity in the upper layer. Dynamical linkage between the localized eddies and large-scale response remains to be clarified in future work.

Seasonal and spatial contrasts of nitrate + nitrite (N + N) concentrations in the slope area (the inshore area to the Kuroshio), Kuroshio and subtropical gyre areas were described by using data sets carried out along the O-line (138°E) between 34°45′N and 30°N over 11 years (2002–2013). The mean concentration of N + N in the surface mixed layer during winter was elevated to 4.8 ± 2.7, 1.5 ± 1.6 and 0.7 ± 0.4 µM in the slope, Kuroshio and subtropical gyre areas, respectively, while it was depleted to < 0.1 µM in all areas during summer. Applying regression analyses to the data, a significant negative correlation between N + N concentration and temperature was found at any depths above 1000 m in both summer and winter in these areas, except for the summer surface depletive layers. The analyses also showed that the diffusive upward flux and the depth difference between the surface mixed layer and the 15-µM nitrate-isoconcentration depth were important factors to induce the seasonal contrast between winter and summer and horizontal contrast among the slope, Kuroshio and gyre areas in the N + N concentration in the surface mixed layer. Since the nitrate-isoconcentration depth is much shallower in the slope area than in the other two areas, the developing wintertime mixed layer reaches to the nitrate-rich water in the slope area, and that leads to a several micromolar increase in the surface N + N concentration there.

The hydrographic structure of a quasi-stationary jet separated from the Kuroshio Extension, a phenomenon that possibly leads to deepening of the winter mixed layer, is revealed via intensive observations using a conductivity–temperature–depth profiler and a ship-mounted acoustic Doppler current profiler (ADCP) carried out in September 2009. Data collected from profiling floats set to drift isopycnal layers and time series of sea surface buoys and satellite altimeters were also analyzed to understand the continuity, water characteristics, and time variation of the jet. Although the flow field was complex due to disturbances such as energetic eddies, the jet transported subtropical water to the downstream (northeastern) observation region in a layer shallower than 400 dbar and its highest velocity was concentrated in the mid- and deep layers (≤0.30 m s−1 at the sea surface and ≥0.05 m s−1 at 800-m depth). The velocity axes of the jet detected from the satellite data corresponded to those detected through analysis of the ADCP data, and the intensity of the jet at the sea surface varies over interannual-to-decadal time scales. Part of the interannual-to-decadal variation in the velocity field of the jet is controlled by the dynamic state of the Kuroshio Extension and is correlated with that of the Kuroshio Extension latitude (linear correlation coefficient r ~ 0.67). The relationship between these variations can be interpreted qualitatively as being responsible for the inertial streamers that separate from the crests of meanders of the Kuroshio Extension to the jet region due to the large steering effect.

The occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll-a concentration (CHL) were examined by generalized additive models for 10-mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food-poor conditions of the Kuroshio Current system could be key to their recruitment success.

Yatsu, A., Chiba, S., Yamanaka, Y., Ito, S-I., Shimizu, Y., Kaeriyama, M., and Watanabe, Y. 2013. Climate forcing and the Kuroshio/Oyashio ecosystem. – ICES Journal of Marine Science, 70: 922–933. The Kuroshio and Oyashio, western boundary currents in the North Pacific, greatly influence climate, ecosystems, and fisheries in the western North Pacific and its adjacent waters. The Kuroshio/Oyashio ecosystem (KOE) shows interannual and decadal variability including regime shifts. Under a collaboration of the Climate Forcing and Marine Ecosystem Response (CFAME) Task Team and Working Group 20 (Evaluations of Climate Change Projections) of PICES, we analysed the observed time-series of physics, nutrients, chlorophyll, zooplankton abundance and phenology, and productivity, biomass, and catch of commercially important species to assess the impacts of Intergovernmental Panel on Climate Change's global change scenarios on KOE. Mechanistic linkages from climate forcing to fish population dynamics were explored for the Japanese common squid (Todarodes pacificus), Japanese sardine (Sardinops melanostictus), walleye pollock (Theragra chalcogramma), and chum salmon (Oncorhynchus keta). Future scenarios of zooplankton, commercial species, and ecosystem changes were presented based on the empirical mechanistic linkages and results of projections for physical conditions and primary production in KOE derived from both empirical knowledge and three-dimensional ecosystem-biogeochemical models. Associated data gaps, uncertainties, and implications for managers were also discussed.

The Fukushima Dai-ichi Nuclear Power Plant accident in March 2011 released radiocaesium (137Cs and 134Cs) into the North Pacific Ocean. Meridional transects of the vertical distribution of radiocaesium in seawater were measured along 147 °E and 155 °E in October–November 2012, 19 months after the accident. These measurements revealed subsurface peaks in radiocaesium concentrations at locations corresponding to two mode waters, Subtropical Mode Water and Central Mode Water. Mode water is a layer of almost vertically homogeneous water found over a large geographical area. Here we show that repeated formation of mode water during the two winter seasons after the Fukushima accident and subsequent outcropping into surface water transported radiocaesium downward and southward to subtropical regions of the North Pacific. The total amount of Fukushima-derived 134Cs within Subtropical Mode Water, decay-corrected to April 2011, was estimated to be 4.2 ± 1.1 PBq in October–November 2012. This amount of 134Cs corresponds to 22–28% of the total amount of 134Cs released to the Pacific Ocean.

To clarify the life histories of two tropical–subtropical Eucalanidae species, Rhincalanus nasutus and Rhincalanus rostrifrons , we investigated the geographical and vertical distributions of their copepodid populations in the northwestern (NW) Pacific Ocean. Zooplankton samples were collected between 15°N and 49°N in the NW Pacific. Rhincalanus nasutus was widely distributed from 20°N to 49°N, whereas R. rostrifrons was restricted to more southerly latitudes (15–37°N). The occurrence of the two species in the surface layer was associated with seasonal spring ontogenetic vertical migration (OVM). Gonadal analysis indicated that, during spring, both species reproduce in the surface layers of the Kuroshio–Oyashio Transition Area (TA) and the slope water area, which is a region of the continental slope situated north of the Kuroshio axis. Our results suggest that both species might have 1 or 2 year life cycles. In comparison, dormant populations occupying the water below the surface layer mainly comprised adult females (50.2% for R. nasutus and 57.7% for R. rostrifrons ), which implied that this is an advantageous strategy for this life state in response to irregular increases of primary production in tropical–subtropical oceans. Furthermore, dormancy in deep waters (500–1000 m) by R. nasutus might indicate a strategy to avoid the relatively high predation risks incurred in shallower waters, due to its larger body size. In contrast, the smaller body size of R. rostrifrons facilitates dormancy in shallower waters (200–500 m depth).

We investigated the geographical and vertical distribution of the copepodid stages of Eucalanus californicus in the northwestern (NW) Pacific Ocean, and compared life history characteristics against the northeastern (NE) population of the species and the neighboring subarctic sister species, Eucalanus bungii . In the NW Pacific, multi-layered zooplankton samples were collected between 15°N and 49°N. High abundances (>1000 inds. m −2 ) of E. californicus were restricted to an area around 33°N, whereas E. bungii was highly abundant between 36°N and 49°N. The occurrence of E. californicus in the surface layer was associated with seasonal spring ontogenetic vertical migration (OVM), as suggested by previous studies in the NE Pacific. Gonadal analysis of adult females showed that surface reproduction occurs during the spring in the slope water area, which is a region on the continental slope north of the Kuroshio axis, and within the Kuroshio–Oyashio Transition Area (TA). The seasonal OVM strategy of E. californicus in the NW Pacific is characterized by (1) shorter periods of surface reproduction and growth and (2) deep C5 stage dormancy (500–2000 m). The former is an adaptive response to relatively high water temperatures and short bloom periods in the TA and slope water area. The latter strategy of deep dormancy is considered to be an adaptation to avoid drift caused by a local oceanic feature of deeper westward (>1000 m) recirculation currents, thus retaining the population within the high primary production zones of the TA and slope water area.

This study investigated temporal variations in the vertical structure and water properties of a warm-core ring that migrated into the western subarctic gyre of the North Pacific, based on analyses of temperature and salinity data derived from two profiling floats, together with shipboard and satellite observation data. The floats were initially deployed into cold and fresh Oyashio water in September 2003, and were entrained into a warm-core ring in October 2003, remaining within the ring until detrainment in December 2004. Drastic cooling and freshening of the upper core water of the ring were observed during the above entrainment of the floats with cold and fresh water into the ring, whereas moderate variations in structure and water properties were observed during a quasi-isolated phase from November 2003 to November 2004 when the ring did not experience major interactions with ambient hydrographic features. The upper part of the core water (upper core), with relatively warm/saline water above 26.6 σ θ , was under the influence of the atmosphere in winter via the formation of a deep mixed layer exceeding 300 dB, and had a prominent pycnostad below the seasonal pycnocline from spring to autumn. In contrast, the lower core, with relatively cold and fresh water below 26.6 σ θ , was not ventilated throughout the observation period. Isopycnal surfaces showed a shoaling trend of about 50 dB/year during the quasi-isolated phase, suggesting viscous decay over a timescale of several years. Markedly cold and thick water was also frequently observed within the ring, indicating the intrusion of water from the Sea of Okhotsk.

The Oyashio region in the western North Pacific supports high biological productivity and has been well monitored. We applied the NEMURO (North Pacific Ecosystem Model for Understanding Regional Oceanography) model to simulate the nutrients, phytoplankton, and zooplankton dynamics. Determination of parameters values is very important, yet ad hoc calibration methods are often used. We used the automatic calibration software PEST (model-independent Parameter ESTimation), which has been used previously with NEMURO but in a system without ontogenetic vertical migration of the large zooplankton functional group. Determining the performance of PEST with vertical migration, and obtaining a set of realistic parameter values for the Oyashio, will likely be useful in future applications of NEMURO. Five identical twin simulation experiments were performed with the one-box version of NEMURO. The experiments differed in whether monthly snapshot or averaged state variables were used, in whether state variables were model functional groups or were aggregated (total phytoplankton, small plus large zooplankton), and in whether vertical migration of large zooplankton was included or not. We then applied NEMURO to monthly climatological field data covering 1 year for the Oyashio, and compared model fits and parameter values between PEST-determined estimates and values used in previous applications to the Oyashio region that relied on ad hoc calibration. We substituted the PEST and ad hoc calibrated parameter values into a 3-D version of NEMURO for the western North Pacific, and compared the two sets of spatial maps of chlorophyll-a with satellite-derived data. The identical twin experiments demonstrated that PEST could recover the known model parameter values when vertical migration was included, and that over-fitting can occur as a result of slight differences in the values of the state variables. PEST recovered known parameter values when using monthly snapshots of aggregated state variables, but estimated a different set of parameters with monthly averaged values. Both sets of parameters resulted in good fits of the model to the simulated data. Disaggregating the variables provided to PEST into functional groups did not solve the over-fitting problem, and including vertical migration seemed to amplify the problem. When we used the climatological field data, simulated values with PEST-estimated parameters were closer to these field data than with the previously determined ad hoc set of parameter values. When these same PEST and ad hoc sets of parameter values were substituted into 3-D-NEMURO (without vertical migration), the PEST-estimated parameter values generated spatial maps that were similar to the satellite data for the Kuroshio Extension during January and March and for the subarctic ocean from May to November. With non-linear problems, such as vertical migration, PEST should be used with caution because parameter estimates can be sensitive to how the data are prepared and to the values used for the searching parameters of PEST. We recommend the usage of PEST, or other

The horizontal transport of calanoid copepod Neocalanus flemingeri, N. plumchrus and N. cristatus in the subarctic North Pacific has been investigated by particle tracking experiments using an ocean circulation model. In our physical numerical model, the current and frontal systems in the subarctic Pacific are reproduced realistically, and fine-resolved (not smoothed) and vertically sheared western boundary currents in the model enable us to assess the differences in horizontal transports among Neocalanus species. In the experiments, seasonal vertical migration and life cycle of Neocalanus species is included, and this attempt is a novel approach in examining the transports of the zooplanktons. The maximal depths of the vertical migrations and the lengths of the surface and mesopelagic dwelling duration are the essential factors in characterizing the trajectory of the horizontal transport. Both small and large forms of N. flemingeri (hereafter NF-SF and NF-LF) whose mesopelagic-inhabited depths are the shallowest among the three Neocalanus species are transported to more distant regions from initial positions compared with the others. The longest transport distance is over 5000 km for NF-SF. On the other hand, the transport distance of the deepest inhabitant N. cristatus (hereafter NC) is the shortest. The differences in the transport distance are due to the current speed of the western boundary currents at the inhabited depth at which they spend most of their lifetime (ca. 3/4 of their lifetime). More than 82% of NF-LF that originated from the Okhotsk Sea completes its life cycle in the Okhotsk Sea, and all the animals out to the Pacific are transported to the south of the subarctic front where their survivals are unexpected due to high temperatures. This is consistent with the observed limited distribution of NF-LF in the Okhotsk Sea and its surrounding waters. Geographical genetic variations of Neocalanus species are reported as very low. This implies frequent genetic exchange all over the Pacific and its adjacent seas. Being consistent with the above, the present study suggests that the trans-Pacific transport of Neocalanus species can be accomplished within a few generations.