Hidekatsu Yamazaki

Tokyo University of Marine Science and Technology · Faculty of Marine Science

Marine aggregates, composed of various particles, play a crucial role in ocean carbon storage. The overall size distribution of the aggregates (number size spectra) is controlled by the balance between aggregation and disaggregation processes. Turbulence has been proposed to facilitate both aggregation and disaggregation by increasing the collision...

Expansion of offshore wind power generation facilities (or offshore wind farm; OWF) has become a social issue for achieving carbon neutrality. One of the problems unique to Japan is the necessity to obtain the consent of fishing rights holders before constructing OWFs. The ultimate goal of the present study is to develop a comprehensive consensus-b...

We assessed spatial and seasonal variabilities of eddy-driven vertical nutrient fluxes, which are essential for maintaining primary production in the upper ocean. A climatological model based on a Regional Oceanic Modeling System (Regional Oceanic Modeling System) coupled with a Nutrient Phytoplankton Zooplankton and Detritus (NPZD) biogeochemical...

Measuring plankton and associated variables as part of ocean time-series stations has the potential to revolutionize our understanding of ocean biology and ecology and their ties to ocean biogeochemistry. It will open temporal scales (e.g., resolving diel cycles) not typically sampled as a function of depth. In this review we motivate the addition...

Plankton ecosystems are complex, multi-trophic networks of biotic and abiotic interactions among physical and chemical components. Still, nutrient-phytoplankton (NP) interactions are in many cases assumed to be representative of higher trophic-level interactions in plankton ecosystems. Here, we investigate the degree to which NP interactions captur...

Mass and heat fluxes in the ocean are important for understanding global ocean dynamics and ecosystems. Estimates of the diapycnal diffusivity (Kρ) are required for quantifying these fluxes. In this regard, one of the key parameters that is required to estimate the diapycnal eddy diffusivity is the “mixing coefficient” (Γ). The diapycnal diffusivit...

This study conducted numerical experiments using a high-resolution numerical simulator to investigate ocean physical structures around coastal structures with considering stratification. To evaluate the effect of coastal structure’s layouts on ocean physical structures, three layout types of cylindrical objects with diameter of 500 m were considere...

We have extended the closure modelling approach for micro-scale variability, as previously applied to NP and NPZ, NPZD systems [1-6], to include fish (F) as a higher-trophic level. As in our previous studies, EH consistently supports the highest trophic level present, which here is F. Although EH itself is not observable, the coefficient of variati...

Conventionally, food web models have been developed based on the mean-field approach ignoring small-scale spatial variability. The closure modelling approach, which accounts for both fluctuations and spatial means, is an effective way to model the impact of heterogeneity on plankton ecosystem dynamics. The hypothesis "Environmental Heterogeneity (E...

Despite suggestions that turbulence can affect the migration of zooplankton, field observations of such effects are scarce. This is especially the case for bottom-associated (demersal) zooplankton that reside in the typically turbulent near-bottom environment. Using moored sensors deployed at two coastal sites in the North Pacific and the Red Sea,...

These first lines of Hensen’s article (Figure 1) in the “Fünfter Bericht” (1887) translate as follows [...]

Spatial patchiness of plankton enhances fishery production and carbon export in the ocean. While diel vertical migration (DVM) has been identified as an important factor contributing to vertical patchiness, its effect on horizontal patchiness has never been investigated. We use a simple individual-based zooplankton model to examine the effect of DV...

Baroclinic (BC) tidal residual circulation due to internal tides is investigated around islands over a shallow ridge using a numerical ocean model. Internal tides enhance vertical mixing over shallow slopes, leading to horizontal density gradients that drive BC residual circulation along the main thermocline. For a strongly stratified summer case,...

Rather than spatial means of biomass, observed overlap in the intermittent spatial distributions of aquatic predators and prey is known to be more important for determining the flow of nutrients and energy up the food chain. A few previous studies have separately suggested that such intermittency enhances phytoplankton growth and trophic transfer t...

Marine aggregates formed through particle coagulation, large ones (>0.05 cm) also called marine snow, make a significant contribution to the global carbon flux by sinking from the euphotic zone, impacting the Earth’s climate. Since aggregate sinking velocity and carbon content are size-dependent, understanding the physical mechanisms controlling ag...

The Kuroshio and tides significantly influence the oceanic environment off the Japanese mainland and promote mass/heat transport. However, the interaction between the Kuroshio and tides/internal waves has not been examined in previous works. To investigate this phenomenon, the two-dimensional high-resolution nonhydrostatic oceanic Stanford Unstruct...

Submersible fluorescence and turbidity sensors are widely used in studies of oceans and lakes. To reduce the instrument size, an overlapping interrogation volume is commonly used for the two sensors. Fluorescence sensors emit blue light for excitation and measure the red light emitted by excited chlorophyll pigments. However, during the night, many...

Previous modeling studies have shown that observed micro-scale (mm) variability of nutrients and phytoplankton biomass can strongly impact the large-scale mean growth response of phytoplankton in ways that cannot be represented by typical models based on the mean field approximation. Also, models accounting for the flexible eco-physiology of phytop...

Abstract: Plankton are microscopic organisms that constitute the sustaining base of food chains in the ocean. Various models have been developed using equations to study their important roles in marine ecology and chemistry. Such models typically assume that plankton respond to changing environmental conditions according to simplistic response equa...

A field campaign was conducted around salmon cages, using a combination of a towed ADCP and a free‐fall multi‐parameter profiler, in order to investigate flow structures and the possible distribution of effluent materials. Two transect observations showed that hydrographic conditions changed dramatically within 5 days, from highly stratified open w...

This paper discusses a turbulent intermittency model introduced in 1990, the B-model. It was found that the original manuscript which introduced the B-model contained a couple arithmetic errors in the equations. This work goes over corrections to the original equations, and explains where problems arose in the derivations. These corrections cause t...

A new Scientific Committee for Ocean Research (SCOR, http://www.scor-int.org/) working group has been formed, entitled SCOR WG-154 “Inte- gration of Plankton-Observing Sensor Systems to Existing Global Sampling Programs (P-OBS, http://www.scor-int.org/SCOR_WGs_WG154. htm.).” The working group (P-OBS WG) is review- ing biological sensing technologie...

This chapter synthesizes progress achieved in the understanding of the dynamics of harmful algal blooms (HABs) under the auspices of the GEOHAB Core Research Project HABs in Stratified Systems. A variety of aquatic environments are considered, where small-scale hydrographic features may be encountered in stratified water columns. A special emphasis...

This study investigates the dynamics of tidally induced internal waves over a shallow ridge, the Izu-Ogasawara Ridge off the Japanese mainland, using a downscaled high-resolution regional ocean numerical model. Both the Kuroshio and tides contribute to the field of currents in the study area. The model results show strong internal tidal energy flux...

This study investigated impacts of internal tdies on oceanic flows and developed a tide prediction system with considering internal tides. Numerical simulations employing SUNTANS show that large internal tide flux in the northern area of Izu-Ogasawara Ridge. The baroclinic kinetic energy excited by internal tides explains 59% of the total kinetic e...

For dynamically consistent, high-resolution, yet cost-effective regional oceanic downscaling modelling, an empirical three-dimensional (3D) density estimate based on publicly available datasets is utilized for the Regional Oceanic Modeling System (ROMS) with simple data assimilation (i.e., TS nudging, where TS stands for temperature and salinity)....

Eddy-driven nutrient transport and associated upper-ocean primary production along the Kuroshio

The three-dimensional numerical model SUNTANS is applied to investigate river plume mixing in Otsuchi Bay, an estuary located along the Sanriku Coast of Iwate, Japan. Results from numerical simulations with different idealized forcing scenarios (barotropic tide, baroclinic tide, and diurnal wind) are compared with field observations to diagnose dom...

The Kuroshio off Japan is accompanied by vigorous eddy and frontal activity both on meso- and submesoscales, which significantly affects the biogeochemical productivity in the upper ocean. We examine the seasonal variability of eddy-induced nitrate transport and resultant biogeochemical response around the Kuroshio using a climatological ROMS-NPZD...

Regional Oceanic Numerical simulations using ROMS with tidal forcing were conducted to investigate tidally induced internal waves (internal tides) in the vicinity of the Izu-chain Islands. The tides enhance the enrgy flux of internal waves by about 10 times as large around the islands. Therefore, in the study region, the internal waves are consider...

The generation of trapped and radiating internal tides around Izu-Oshima Island located off Sagami Bay, Japan, is investigated using the three-dimensional Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator (SUNTANS) that is validated with observations of isotherm displacements in shallow water. The model is forc...

The Kuroshio is one of the most energetic western boundary currents accompanied by vigorous eddy activity both on mesoscale and submesoscale, which affects biogeochemical processes in the upper ocean. We examine the primary production around the Kuroshio off Japan using a climatological ocean modeling based on the Regional Oceanic Modeling System (...

While swimming organisms may cause turbulence, it is not clear how strong the turbulence is and if eddies are large enough to mix stratified water columns. We conducted an observational experiment in a large aquarium tank containing several thousand Japanese sardines Sardinops melanostictus. Turbulence data were collected from inside the sardine sc...

Harmful algal blooms (HABs) are natural phenomena that result from the interplay of biological, chemical, physical, and sedimentary processes occurring at different temporal and spatial scales. This paper provides an integrated description of HAB dynamics occurring at the mesoscale (10–100 km, sensu Haury et al., 1978) in confined and semi-confined...

Numerical simulations of sediment resuspension due to shoaling internal bores are performed with a nonhydrostatic model, SUNTANS. Results show strong sediment resuspension induced by internal bores and a turbidity layer intruding offshore in the interior of the water column, known as an intermediate nepheloid layer (INL). Sediment resuspension proc...

The Kuroshio is one of the most energetic western boundary currents accompanied by vigorous eddy activity both at meso- and submesoscales which significantly affect biogeochemical productivity in the upper ocean. We examine such processes with a climatological ocean modeling based on ROMS coupled with an NPZD model for the Kuroshio region off Japan...

We have developed a free-fall multi-parameter profiler (YODA Profiler) to measure various physical and biological parameters in coastal ocean. We found internal bores create a strong mixing event. Sediment resuspension is associated with the mixing event and also AZFP detected fish school at the front of bore. We have deployed a cable observatory s...

Highly intermittent spatial variability of phytoplankton is observed ubiquitously in marine ecosystems, especially when measurements are performed at the micro-scale level. Therefore, theoretical developments and new modelling tools are required to understand the observed small-scale vertical structure and its relationship to ecosystem behaviour. N...

We observed the formation of an internal bore interacting with the vertically-sheared flow generated during the previous phase of the internal tide, which resulted in strong turbulent mixing. The rate of turbulent kinetic energy dissipation reached on the order of 10-5 W kg-1 during the event. Numerical simulations reproduced the observed interacti...

The annual overturn of lake water (termed holomixis) during winter is essential in maintaining the environment of warm monomictic lakes by transporting heat and organic and inorganic constituents; however, direct observation of wintertime mixing processes is limited. To better understand the detailed physical processes responsible for holomixis, th...

Coastal ocean environment exhibits rapid change in time and space. Continuous long term measurements of environmental data are scarce. Environmental parameters, such as temperature and salinity, change due to multi-scale physical processes, such as Kuroshio and internal waves. A different scale of physical process affects planktonic ecosystem diffe...

植物プランクトン，凝集体及び動物プランクトンの微細な分布構造を計測するためにさまざまな計測器を開発してき た．本稿はこれらの測器の総説である．さらに現在，沿岸域のプランクトンの多様性を調べることを目的としたCREST プロジェクトで開発しているケーブルオブザバトリと自律型無人潜水機について紹介する． New sampling methods have been developed in order to investigate micro-scale distribution of phytoplankton, marine aggregate, and zooplankton. This article reviews these new technologies. We also int...

The annual overturn of lake water (termed holomixis) during winter is essential in maintaining the environment of warm monomictic lakes by transporting heat and organic and inorganic constituents; however, direct observation of wintertime mixing processes is limited. To better understand the detailed physical processes responsible for holomixis, th...

In this study, a Navis-MicroRider microstructure float and an EM-APEX float were deployed along the Kuroshio Extension Front. The observations deeper than 150 m reveal widespread interleaving thermohaline structures for at least 900 km along the front, presumably generated through mesoscale stirring and near-inertial oscillations. In these interlea...

Observations of the run-up of internal bores in a shallow bay were made with a tow-yo instrument and mooring arrays with high spatial and temporal resolution. Shoreward propagating internal bores have been studied with laboratory experiments and numerical models, but few observational studies have shown the detailed structure of the run-up of inter...

Improved models have recently been developed of flexible physiology and adaptive changes in eco-physiological traits and trait diversity. Like nearly all theoretical descriptions and models of plankton dynamics, these trait-based models are still formulated at the macroscopic level, assuming uniform micro-scale distributions of organisms and their...

The JCOPE2-ROMS downscaling oceanic modeling system improves mesoscale reproducibility by introducing a simple restoration to data which we call “TS (temperature and salinity) nudging”, where the prognostic temperature and salinity fields are weakly nudged four-dimensionally towards the assimilative JCOPE2 reanalysis (Uchiyama et al., 2012). Howeve...

A newly developed tow-yo profiler (YODA Profiler) and a fully nonhydrostatic numerical model, SUNTANS, are used in this study to investigate river plume mixing in Otsuchi Bay, a ria estuary located in Iwate, Japan. Several field campaigns were conducted in the bay during early summer, late summer, and late winter. The YODA Profiler reveals fine fea...

near Joga-shima, Japan, we deployed two microstructure profilers, TurboMAP-L and the TurboMAP-Glider, to obtain vertical and quasi-horizontal measurements of turbulence and chlorophyll a fluor-escence. The deployments were clustered at two stations (one near the coast and another further offshore). Both instruments carried two fluorescence sensors...

This study describes the development of a new tethered quasi-horizontal microstructure profiler: the Turbulence Ocean Microstructure Acquisition Profiler-Glider [TurboMAP-Glider (TMG)]. It is a unique instrument, capable of measuring ocean microstructure (temperature and turbulent velocity shear), chlorophyll, and turbidity simultaneously through a...

The goal of this study is to make it possible to measure the distribution of the plankton by using an AUV with a digital microscope camera on the nose. Because of the relatively low performance of the storage device in our AUV, the Regions Of Interest (ROIs) that contain focused plankton' images are extracted from a grabbed image in realtime, and o...

See the attached file.

The measurement of phytoplankton distributions in ocean ecosystems provides the basis for elucidating the influences of physical processes on plankton dynamics. Technological advances allow for measurement of phytoplankton data to greater resolution, displaying high spatial variability. In conventional mathematical models, the mean value of the mea...

The Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) program of the Scientific Committee on Oceanic Research (SCOR) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, was created in 1999 to foster research on the ecological and oceanographic mechanisms underlying the population dynamics of harmful algal blooms (HABs...

We have developed a new tethered quasi-horizontal microstructure profiler: TurboMAP-Glider (TMG). It is a unique instrument, capable of measuring ocean microstructure (temperature and turbulent velocity shear), chlorophyll and turbidity simultaneously through a quasi-horizontal perspective. We carried out three field experiments near Joga-shima (Ja...

A 48-h microstructure experiment captured the variation of turbulence in Lake Biwa, Japan, during a strong stratification period, 1 week after a typhoon event. A free-fall microstructure profiler (TurboMAP) and a fine-scale profiler (F-probe) were deployed. An array of five ADCPs positioned close to the experiment site provided current measurements...

The overall objective of the Core Research Project (CRP) “Harmful Algal Blooms in Stratified Systems” of the Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) programme was to determine the factors underlying the formation, maintenance and dissipation of harmful algal blooms (HABs) in stratified systems. In the last 20 years, investi...

We have developed a Lagrangian model to investigate a potential mechanism based on phototaxis behavior of phytoplankton cells for the formation of thin layers. We assume that all cells follow a time-regulated diurnal vertical migration during which they experience photo-acclimation based on the Denman and Marra (1986) model. When a cell experiences...

Direct observations of microstructure near the Kuroshio Front were conducted in August 2008 and October 2009. These show negative potential vorticity (PV) in the mixed layer south of the front, where directly measured turbulent kinetic energy dissipation rates are an order magnitude larger than predicted by wind-scaling. These elevated dissipation...