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Since the early 1970s, many artificial reefs (ARs) have been deployed in Japanese coastal waters to create fisheries grounds. Recently, researchers began to use environmental DNA (eDNA) methods for biodiversity monitoring of aquatic species. A metabarcoding approach using internal standard DNAs [i.e., quantitative MiSeq sequencing (qMiSeq)] makes it possible to monitor eDNA concentrations of multiple species simultaneously. This method can improve the efficiency of monitoring AR effects on fishes. Our study investigated distributions of marine fishes at ARs and surrounding stations in the open oceanographic environment of Tateyama Bay, central Japan, using qMiSeq and echo sounder survey. Using the qMiSeq with 12S primers, we found higher quantities of fish eDNAs at the ARs than at surrounding stations and different fish species compositions between them. Comparisons with echo sounder survey also showed positive correlations between fish eDNA concentration and echo intensity, which indicated a highly localized signal of eDNA at each sampling station. These results suggest that qMiSeq is a promising technique to complement conventional methods to monitor distributions of multiple fish species.

協力学習理論では学びの経験の具体性と学習者間の同一性（特に話の文脈の共有し合い）とが軽視されている。協力学習の方法を継承する「協調学習」の研究においても、コミュニケーションは当面の課題に即して理解され、当面の課題とは関係していないとみなされる場面や側面への関心が弱くなる。そこでは、学習者間の差異や同一性が研究者や教師の関心のみに基づいて認識され、学習者間の同一性（または差異と同一性との関係）の孕む問題点が度外視されてもいる。今後は、学習者間のどのような同一性、特に話の文脈のどのような共有し合いが、または学習者間の差異と同一性とのどのような関係が学びの促進に寄与するかを、小集団学習の場面において日常的に存在し生成している差異や同一性にも着目して検討しなければならない。例えば、学習者自身が学習者間の差異や同一性をどう認識しうるかについて考慮されなければならない。

木稿では、中学3年生の教室における或る小集団の会話の事例を検討する。当該小集団はいわゆるT字型になっており、「虐待の連鎖」に関する会話が、身体や物や空間のありようと相関して生徒間の差異と同一性との多元的関係として生成していた。生徒聞の差異だけではなく、生徒聞の同一性や、生徒聞の差異と同一性との関係をも問題にすることは、生徒間の協力や協調性を実現するための生徒指導の方法を考察する上でも重要であると考えられた。また、当事者聞の差異と同一性との多元的関係を精織に分析するための理論的枠組みについても、前述のT字型の小集団における会話の事例を踏まえつつ考察した。そこからは、協力学習(Cooperative learning) の理論的課題や、「協調学習」といわれる学習科学における協同学習 (collaborative learning)の理論的課題についての示唆も得られた。

In this study, direct continuous measurements of deep-sea turbulent flows near the seafloor were made in the Izena Cauldron hydrothermal fields, Okinawa Trough, Japan, to understand the dynamics of the bottom mixed layer. The objectives of this study were to reveal time series fluctuations of deep-sea turbulence intensity, that is, the turbulence energy dissipation rate, using an expendable vertical microstructure profiler (VMP-X), and to correlate them with in situ environmental data (flow, turbidity, conductivity, temperature, and depth data) obtained from a monitoring station installed on the seafloor near the VMP-X observation point. The turbulence energy dissipation rate ( $\boldsymbol{\varepsilon}$ ) value near the seafloor changed from 10−10 to 10−7 W kg−1, and $\boldsymbol{\varepsilon}$ maxima were observed from a flood tide between ebb tides (13:00–15:30 and 20:30–23:00) around a depth of 960 m, whereas the $\boldsymbol{\varepsilon}$ values decreased to 10−9 W kg−1 during ebb tide. In the former case, the water temperature increased only slightly, but in the latter case, water temperature increased by 0.1 °C. Furthermore, the turbulent flow was relatively strong from the seafloor to a height of around 50 m from the bottom. Turbulent flow observation points were located to the west of the hydrothermal vent area. The bottom topography of this area is closed. Deep-sea current data were successfully obtained for the layers between the seafloor and 60 m above the bottom, and periodic fluctuations with east–west and north–south components were synchronously observed with water-level variations. According to these environmental data and complex (closed) bottom topography data, the increasing water temperature fluctuation may occur as a result of hydrothermal venting (transport or intrusion of warm water). Therefore, $\boldsymbol{\varepsilon}$ may be affected by hydrothermal venting. However, to better understand the dynamics of vertical mixing processes, more observational data, such as continuous turbulent flow data, are necessary. In future studies, we will collect and analyze more spatiotemporal field data using VMP-X to understand the dynamics of the bottom mixed layer and improve the accuracy of numerical models.

In this study, time series measurements of turbulent flows near the sea floor were taken at hydrothermal fields in the Okinawa Trough. The purpose of this study was to understand the dynamics of the bottom mixed layer (BML), reveal fluctuations in the time series of deep sea turbulent flows (the turbulent energy dissipation rates) using VMP-X, and correlate them with in-situ flow, turbidity, and conductivity, temperature, and depth data obtained from a monitoring station on the sea floor. At the Kumejima west field, time series fluctuations in turbulent energy dissipation rate () between the sea surface and the seafloor were successfully measured. The near the sea bottom changed from 10–10 to 10–7 (W kg-1) and the maximum was observed from a flood tide between ebb tides, and decreased to 10–9 (W kg-1) during the ebb tide on June 24. Moreover, the turbulent flow was relatively strong from the seafloor to a height of around 80 m above it, and water temperature rose 0.1–0.2 degrees Celsius. The measurement points were located approximately 900 m to the northwest of the hydrothermal vent area. Deep-sea current data were successfully recovered for the layers at depths between the seafloor and 30 m above it, and a periodic fluctuation with an amplitude of approximately 10 cm/s for the east-west and north-south components, which was synchronized with variations in the water level, was also observed. According to these environmental and complex bottom topography data, this characteristic water temperature fluctuation may occur as a result of hydrothermal venting (transport or intrusion of warm water). Therefore, the intensity of turbulence may also be affected by hydrothermal venting. However, further continuous in-situ observational data are necessary to understand the dynamics of the BML. In a future study, we will collect and analyze more spatiotemporal turbulent flow data to understand the dynamics of the BML and improve the accuracy of the numerical model.

In this study, the current fluctuations were measured at the hydrothermal fields in the Okinawa Trough (Hatoma Knoll, Irabu Knoll, and Iheya North field) to characterize the fluid environment. The purpose of this study was to reveal the fluctuations of the deep-sea currents using an acoustic Doppler current profiler (ADCP), and to correlate them with the development of a bottom mixed layer as predicted by a numerical model. An ADCP (Teledyne RD Instruments Workhorse Sentinel, 300 kHz) was installed on the seabed at the Hatoma Knoll (depth about 1500 m), Irabu Knoll (depth about 2000 m), and Iheya North field (depth about 1000 m). For each observation point, the deep-sea current data were successfully recovered in the layer at depths between the seafloor and 40–60 m above the seafloor. Notably, the measurement results obtained at the Hatoma Knoll and Iheya North field showed a remarkably interesting fluctuation. During a time period of approximately 3 h, the range in the depths at which the currents were successfully recorded increased in a pulse form, up to around the upper layer at 120 m, allowing measurements in almost all of the layers. The time period of this pulse corresponded to the shift from an ebb tide to high tide. With the exception of these pulses, the currents could only be recorded from the seafloor to about a 40 m layer. This result indicated that a suitable environment for ADCP measurements was formed only within this range. To investigate the cause, a numerical model experiment was performed for the bottom turbulence and subsequent occurrence of vertical mixing of the suspended particulate matter in the Okinawa Trough using a large-eddy simulation (LES) model. The simulated results suggested that the semidiurnal tide periodically enhances the bottom turbulence at intervals of approximately 6 h, with the result that the bottom mixed layer thickness increases to a maximum of approximately 40–60 m. It was concluded that a suitable environment for ADCP measurements near the deep seafloor was formed mainly by the bottom mixed layer corresponding to the tide.

Large eddy simulation (LES) of the resonant inertial response of the upper ocean to strong wind forcing is carried out; the results are used to evaluate the performance of each of the two second-order turbulence closure models presented by Mellor and Yamada (Rev Geophys Space Phys 20:851–875, 1982) (MY) and by Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) (NN). The major difference between MY and NN is in the formulation of the stability functions and the turbulent length scale, both strongly linked with turbulent fluxes; in particular, the turbulent length scale in NN, unlike that in MY, is allowed to decrease with increasing density stratification. We find that MY underestimates and NN overestimates the development of mixed layer features, for example, the strong entrainment at the base of the oceanic mixed layer and the accompanying decrease of sea surface temperature. Considering that the stability functions in NN perform better than those in MY in reproducing the vertical structure of turbulent heat flux, we slightly modify NN to find that the discrepancy between LES and NN can be reduced by more strongly restricting the turbulent length scale with increasing density stratification.

Bispectral analysis of the numerically reproduced spectral responses of the two-dimensional oceanic internal wave field to the incidence of the low-mode semidiurnal internal tide is performed. At latitudes just equatorward of 30°, the low-mode semidiurnal internal tide dominantly interacts with two high-vertical-wavenumber diurnal (near inertial) internal waves, forming resonant triads of parametric subharmonic instability (PSI) type. As the high-vertical-wavenumber near-inertial energy level is raised by this interaction, the energy cascade to small horizontal and vertical scales is enhanced. Bispectral analysis thus indicates that energy in the low-mode semidiurnal internal tide is not directly transferred to small scales but via the development of high-vertical-wavenumber near-inertial current shear. In contrast, no noticeable energy cascade to high vertical wavenumbers is recognized in the bispectra poleward of ∼30° as well as equatorward of ∼25°. A new finding is that, although PSI is possible equatorward of ∼30°, the efficiency drops sharply as the latitude falls below ∼25°. At all latitudes, another resonant interaction suggestive of induced diffusion is found to occur between the low-mode semidiurnal internal tide and two high-frequency internal waves, although bispectral analysis shows that this interaction plays only a minor role in cascading the low-mode semidiurnal internal tide energy.

[1] The distribution of wind-induced internal wave energy in the world's oceans is investigated using a full three-dimensional primitive equation model. Special attention is directed to the global energy input to the surface near-inertial motions and the subsequent downward energy propagation into the deep ocean. We find that the model results for near-inertial energy in the oceanic mixed layer, depth-integrated horizontal energy fluxes, and vertical structures of WKB-scaled kinetic energy are all consistent with the available observations in the regions of significant wind energy input and that the annual mean of the global wind energy input becomes ∼0.4 TW. It is also found that most of the wind-induced energy resides in high vertical modes, 75–85% of which is dissipated in the surface 150 m. The present study therefore predicts that the total wind-induced near-inertial energy available for deep-ocean mixing is limited to, at most, 0.1 TW, which is an order of magnitude smaller than previously estimated. Adding the energy flux from tide-topography interactions of ∼0.9 TW, we can conclude that the total energy available for deep-ocean mixing is ∼1.0 TW, obviously falling short of the required power to sustain the global overturning circulation. This might suggest the existence of other important energy sources, such as the one through geostrophic adjustment processes, and/or additional mechanisms sustaining the global overturning circulation, such as effects of Ekman upwelling in the Southern Ocean. Another possibility is that previous estimates of the volume transport of the global overturning circulation might be too large.