Spatiotemporal structures of tidal and mean currents in August 2008 and May 2010 were estimated by shipboard ADCP data around the Hachiri-ga-se marine hill in the southwestern Japan Sea. The time variations of the tidal currents were quite similar both in August and May. The vertical structure of tidal and mean currents in August was more baroclinic than that in May. Upwelling region moved when the

Seasonal variations in vertical mixing intensity in the intermediate layer of the northern Okinawa Trough was deduced using the seasonal variations in salinity in the North Pacific Intermediate Water (NPIW) using two distinct datasets: the World Ocean Atlas 2013 and historical conductivity, temperature, and depth data in the Okinawa Trough. Water mass analysis of the NPIW with a simple advection model

Vertical mixing in the ocean is an important physical process that brings deep nutrients to the upper layer. The Tokara Strait, where the Kuroshio flows out to the North Pacific from the East China Sea, is known for a mixing hotspot, but the associated vertical nutrient transport has not been well quantified yet, especially in the intermediate layer below 200 m depth. This study involved flow, turbulence

We investigate the control mechanisms of the deep Pacific Ocean circulation by introducing updated methods for parameterizing tidal mixing. The column-integrated rates of dissipation in near- and far-fields are derived from the tidal energy conversion and dissipation rates estimated by a high resolution tide model. In the calculation of the far-field mixing, its dependency on stratification is taken

While the Kuroshio is known to be a nutrient stream, as these nutrients are in dark subsurface layers, they are not immediately available for photosynthesis unless they are supplied to the sunlit surface layers. Recent microstructure observations have revealed that strong diapycnal mixing caused by the Kuroshio flowing over topographic features and double diffusion in the subsurface layers of the Kuroshio

In the stratified ocean, vertical eddy diffusivity in the subsurface pycnocline plays a major role in new production through transporting nutrients upwards from the darker/nutrient-rich layer. In order to evaluate the diffusivity that was less available in the subsurface layers where indirect estimations are difficult, we conducted direct microstructure measurements in the upper 300 m of the open Pacific

Sea straits are known for important sites to modify water-mass properties and transport nutrients through vigorous vertical mixing. The first microstructure measurements ever taken in the Tsugaru Strait, between the Sea of Japan and the Northwest Pacific Ocean, showed elevated turbulent mixing. The turbulent energy dissipation rate was especially enhanced to O(10−6 W kg−1) via an internal hydraulic

Vertical mixing in oceans is an essential component of the dynamics of ocean circulation, including meridional circulation. Nevertheless, various aspects of mixing, particularly in conjunction with global ocean energetics, remain debatable. One of the biggest reasons is the lack of observational facts. With the recent expansion of global vertical-mixing observations, attempts have been made to estimate

Vertical turbulent nitrate fluxes were estimated in the western North Pacific from direct measurements of vertical turbulent mixing and vertically continuous nitrate profiles during the summer of 2008. We made three north–south transects that covered the area from the subarctic to the subtropics including a section along the Emperor Sea Mounts. Subsurface fluxes generally showed an increasing trend

This study examined characteristics of near-inertial internal waves (NIWs) associated with the background mesoscale field near the Tsushima Warm Current. Observational stations off Sado Island were visited recurrently to assess spatiotemporal changes of fine-scale and microscale properties of seawater. Also, NIWs were inspected in terms of relative vorticity and total strain in surface geostrophic

We conducted a ship observation of two anticyclonic mesoscale eddies (Eddies A and B) between June and July 2016 in the offshore region of the western subarctic North Pacific to clarify the impact of anticyclonic eddies on biological production. Analysis of satellite data reveals that Eddy A formed south of the Alaskan Peninsula on May 2011 while Eddy B formed in the observation area on November 2015

The measurement of turbulence is necessary to quantify the vertical, diapycnal transport of heat, water and substances influencing climate, nutrient supply and marine ecosystems. As specialist instrumentation and ship-time are required to conduct microstructure measurements to quantify turbulence intensity, there is a need for more inexpensive and easy measurement methods. This study demonstrated that

The effects of eddies on the subduction and movement of water masses reaching the 137\(^{\circ }\) E section are examined in a nominal 10-km resolution ocean general circulation model using a backward-particle tracking method. Target water masses are the Tropical Water (TW), the Eastern Subtropical Mode Water (ESTMW), the Subtropical Mode Water (STMW), and lighter variety of the Central Mode Water

The subtropical North Pacific has been historically considered as a stable and homogenous oligotrophic marine ecosystem. The consistently low phytoplankton biomass has been attributed to a close balance between phytoplankton growth and grazing mortality. However, phytoplankton summer blooms were frequently observed in the central North Pacific near the Hawaiian Islands. To determine whether this is

Decadal-scale variability of the North Pacific subtropical mode water (STMW) and its influence on the pycnocline are examined by analyzing Japan Meteorological Agency (JMA) repeat hydrographic observations along the 137°E meridian from 1972 to 2019, with a particular focus on the summer season when the seasonal upper pycnocline develops above the STMW. The STMW appears between 20° and 32°N at 137°E

The dissolved (d) and total dissolvable (td) trace metals were determined in seawater samples collected from the East China Sea (ECS). Labile particulate (lp) species was calculated as td minus d, and the sectional and vertical distributions of d and lp trace metals were evaluated. The surface concentrations of dAl, dCo, dNi, dCu, and dPb were higher in the continental shelf region than in the Kuroshio

Ocean acidification is likely to impact marine ecosystems and human societies adversely and is a carbon cycle issue of great concern. Projecting the degree of ocean acidification and the carbon-climate feedback will require understanding the current status, variability, and trends of ocean inorganic carbon system variables and the ocean carbon sink. With this goal in mind, we reconstructed total alkalinity

Using a coastal assimilation model, generation mechanism of unusually high sea level (UHSL) at the south coast of Japan in September 2011 is investigated. Both model results and tide gauge observations indicate that sea level rise associated with the UHSL event occurred twice in the middle and end of September. The first one, which is localized around the eastern part of the Seto Inland Sea, is caused

Japan Sea Intermediate Water (JSIW) is in the salinity-minimum layer present between the thermocline and deep water in the Japan Sea. Annual shipboard measurements over the past 20 years revealed that JSIW rapidly freshened in the 2010s, particularly from 2010 to 2011, from 2012 to 2013, and from 2015 to 2016. The mean rate of salinity change at σθ = 27.16 kg m−3 (σθ indicates potential density minus

The effects of diatom abundance and biogenic silica (BSi) deposition on the population growth of tintinnid ciliates were investigated using incubations of sub-surface waters (10 m depth) of Suruga Bay, Japan in April and November 2018. Seawater for incubation was pre-filtered using a 200-µm mesh to remove mesozooplankton grazers. Initial concentrations of dissolved inorganic nitrogen were similar in

The wavenumber spectra of the chlorophyll “a” concentration (Chla) and the sea surface temperature (SST) were obtained from the data of the shipborne fluorometer and satellite measurements in the area of the anticyclonic eddy in the South China Sea in February—March 2004. In the southwestern part of the eddy, the slope of SST spectrum, received from the ship data was − 2.6 ± 0.1 at scales of 3–110 km

The original article can be found online.

Sea ice variations in the severe winter of 2009–2010 in the Bohai Sea are simulated with a coupled ocean and ice model. The modelled ice coverage shows good agreement with satellite observations. Integrated over three sub-regions [the extended Liaodong Bay (LDB), Bohai Bay, and Laizhou Bay], the temporal variations of ice volume and surface air temperature are well correlated at time scales of 5–15 days

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 DVM on the horizontal patchiness of four zooplankton

Hadal, > 6000 m deep shipborne Sea-Bird Electronics SBE 911plus Conductivity Temperature Depth (CTD) data are obtained using two different systems in the vicinity of the Earth’s deepest point, in the Challenger Deep, Mariana Trench 14 years apart. Below 7000 m in very weakly density stratified waters, the salinity data from both sets show an artificial increase with depth of about 10–6 g kg−1 m−1 that

A compilation of surface water nutrient (phosphate, nitrate, and silicate) and partial pressure of CO2 (pCO2) observations from 1961 to 2016 reveals seasonal and interannual variability in the North Pacific. Nutrients and calculated dissolved inorganic carbon (DIC) reach maximum concentrations in March and minimum in August. Nutrient and DIC variability is in-phase (anti-phase) with changes in the

A long-term increasing trend in the transport of the Japan Sea Throughflow is observed from sea-level differences across the Tsushima Strait. Tidal gauge observations show sea level at Hakata, Japan, increasing at a higher rate than that at Busan, Korea. Numerical modeling results suggest that this increasing trend is forced by a northward shift in the Kuroshio axis. As the Kuroshio axis moves northward

Effective water quality monitoring of coastal areas through the measurement of Chlorophyll-a (Chl-a) has remarkably progressed by ocean color remote sensing. Among different sensors, Moderate Resolution Imaging Spectroradiometer (MODIS) Level 3 products provide reliable global representations of the Chl-a concentration. On the other hand, due to the coarse spatial resolution of MODIS data, its applicability

Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike labile trace elements, noble gases are inert and do not react with other substances in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were discharged mainly from the central Indian midocean ridge, convergent boundaries, and the Pacific Ocean via

It is necessary for air–sea interaction and climate research to evaluate heat and salinity transport between the mixed layer (ML) and the permanent pycnocline and its contribution to the ML properties. The authors have calculated the obduction and subduction rates with the Eulerian definition using a 1°-grid Argo dataset and incorporated the obduction rate into the ML budget analysis in order to assess

Habitat heterogeneity is one of the major factors shaping community structure and diversity of many fauna. The present study aimed to reveal the influence of habitat heterogeneity on the nematode community structures and diversity in a seasonally hypoxic bay (Omura Bay of Nagasaki in Western Kyushu, Japan). The severity of hypoxia varies typically along north–south axis of the bay, which is intensified

Significant wave height (SWH) is an important wave parameter that is related to near-shore activities and research on the phenomenon near the air-sea interface. Here, we proposed a new method for retrieving SWH from C-band Sentinel-1 synthetic aperture radar (SAR) interferometric wide mode data based on convolutional neural network (CNN), which can directly establish the empirical relationship between

Equilibrium beach profiles are explained in the context of a thermodynamic theory in which energy dissipation rate due to shoaling waves is extremized through a variational principle. The issue of whether this extremum corresponds to a maximum or a minimum of the action integral under the assumptions made is answered by computing the second variation of the integral around the equilibrium profile:

Parametric cyclone wind models with storm characteristics derived from statistical representation do not agreeably delineate the wind field in the East China Sea, leading to uncertain errors in the numerical simulations of Typhoon waves. A new approach to adjust the cyclone wind field in the framework of the Holland model is proposed. The radius of maximum wind speed and the logarithmically varied

Eddy kinetic energy (EKE) in the Celebes Sea (CS) is investigated using a global, eddy-resolving, ocean general circulation model (OGCM) output. The OGCM simulation shows that a strong EKE is confined in the upper 300-m layer. The period of EKE variability varies with depth. In the 0–100-m layer, EKE has a distinct annual cycle that is strong in winter (December–February) and weak in summer (June–August)

Insufficient in situ observations in high winds make it difficult to verify climatological data sets and the results of tropical cyclone (TC) simulations. Reliable data sets are necessary for developing numerical models that predict TCs more accurately. This study attempted to compare the third-generation Japanese Ocean Flux Data Sets with Use of Remote-Sensing Observations (J-OFURO3) data, with TC

The spatial and temporal decorrelation scales of sea surface salinity (SSS) have been calculated in the tropical Indian ocean from the satellite measurements including Soil Moisture and Ocean Salinity (SMOS), Aquarius, Soil Moisture Active Salinity (SMAP), and the model output data for the period of 2011–2017. The differences in spatial and temporal scales from different products are discussed and

Two zonal high-density hydrographic sections along 41° N and 37.5° N east of Japan were occupied in April 2013 and June 2016 to examine the formation of Central Mode Water (CMW) and Transition Region Mode Water (TRMW) in relation to fronts and eddies. In the 41° N section traversing the meandering subarctic front, the denser variety of CMW (D-CMW) and TRMW was formed continuously on both sides of the

Antarctic coastal polynyas provide extremely dense water to the global abyss, but the dense water formation process has been poorly monitored in winter. This study developed a new tethered profiler to realize time-series observations of the water column in the Cape Darnley Polynya, East Antarctica. The system successfully obtained temperature and salinity profiles at 10-day intervals from March to

The Oyashio–Kuroshio Transitional Region (OKTR) is a nursery ground for pelagic fishes; thus, community succession of mesozooplankton is pivotal to understand prey availability, and it subsequently affects recruitment success. We investigated the surface distribution, biomass, and species composition of thaliaceans (salps and doliolids) that potentially have a significant impact on the food web and

Stygiopontius copepods (Dirivultidae, Siphonostomatoida, Crustacea) are among the most successful meiobenthic organisms at deep-sea hydrothermal vents. Most of their ecology is not yet known, including the spatiotemporal differences in their sex ratios and their controlling factors. We investigated spatial variation in the sex ratio of adult Stygiopontius senokuchiae and its association with environmental

Particulate carbon is one of the major carbon forms in seawater, thus plays an important role in the carbon cycle. Limited small scale studies showed that particulate inorganic carbon (PIC) content was much higher than particulate organic carbon (POC) in the Yellow River Estuary. This study is to test the hypothesis that surface PIC is significantly higher than POC in the Yellow-Bohai Sea (YBS). Using

Surface current velocity from high-frequency radar data are used to study tidal currents in the Mid-Atlantic Bight, which represent an average 32% of the total kinetic energy of the surface circulation. Average annual and seasonal tidal current characteristics and the associated variance of the semi-major axis are computed. The M2 constituent dominates the tide, representing a maximum of 72.26% and

Due to the ubiquitous steep continental shelf slope in the East China Sea, topographic Rossby waves are very common when the Kuroshio Current flows along the slope, and of great importance in the water and energy exchange between the open ocean and coastal sea. To examine the structural characteristics of topographic Rossby wave, we use stretching transform of time and space and perturbation method

Two-years of data from an array of pressure-sensor equipped inverted echo sounders (PIESs) deployed across the Kuroshio east of Taiwan are analyzed in this study. Cross sections of temperature, absolute, barotropic and baroclinic velocities, as well as time series of volume transports and maximum velocity axis location are analyzed to better understand the response of the Kuroshio to local arrivals

The present study aims to reveal the influence of path fluctuations of the western boundary current (Kuroshio) and other regional environmental factors on coastal recruitment of transported organisms. As a model species, we chose a catadromous eel species, Japanese eel Anguilla japonica, which is transported poleward by the Kuroshio in early life stages. We analyzed a 50-year record of A. japonica

River plumes are an important component of estuarine circulation and have a vital role in the transport of estuarine material and momentum balance. However, little information is available on the influence of mouth bars on estuarine plumes. To address this, momentum balance analysis was carried out using the ocean numerical model, to analyze the dynamic characteristics of the Pearl River plumes. The

To elucidate how variables of the seawater CO2 system in surface waters have been changing seasonally and the mechanisms responsible for these changes in the area off the south coast of central Honshu Island, Japan, we made time-series measurements of total dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic macronutrient and chlorophyll a concentrations as well as temperature and salinity

This study investigates the response of surface chlorophyll (CHL) to mesoscale eddies generated in the eastern South China Sea (ESCS) during their lifecycles based on global eddy dataset and chlorophyll data from January 2003 to December 2016. The results show that the responses of CHL anomalies to cyclones are stronger than anticyclones generated in the Luzon Strait (LS) and in the area off northwest

The cold, low-salinity, and nutrient-rich Zhe-Min Coastal Water (ZMCW), an important part of the China Coastal Current, plays a key role in the hydrodynamics, biogeochemical processes and marine ecosystem in the Taiwan Strait (TWS). In this study, the long-term characteristics of the ZMCW were investigated using available data sets, including merged satellite-derived sea surface temperature (SST) data

Dissolved organic matter (DOM) can be partially converted into particulate organic matter via aggregation. Although surface coagulation by bubbles is known to be an aggregation process, a few studies have tested its efficacy for aggregating natural DOM. In the research described here, we tested surface coagulation by bubbles using natural seawater collected from different locations, and achieved organic

The focus of this study was first to determine the most suitable geophysical correction models for obtaining satellite-derived sea level height time series in the South China Sea (SCS; 0–26° N, 99° E–121 °E). Analysis of difference of the sea level anomaly standard deviation was conducted to assess the quality of the various correction models. The set of correction models was used to establish the

A meteo-tsunami is a tsunami-like phenomenon excited by a traveling atmospheric disturbance. In Japan, meteo-tsunamis are frequently observed along the western coast of Kyushu Island during winter–spring. One of the largest meteo-tsunamis occurred on March 3, 2010, where the maximum amplitude of water level oscillations exceeded 1 m in various bays on the western coast of Kyushu Island including Nagasaki

A paper by Zhao and Li that was recently published in this journal (J Oceanogr 75:207–223, 2019) presented the dependence of wind stress across an air–sea interface on wave states. The purpose of these comments is to demonstrate that the sea surface roughness formula proposed by Zhao and Li can also be applied to estimate the sea surface roughness based on wind and wave statistics. The average statistical

We constructed parameterizations for the estimation of dissolved inorganic carbon (DIC) and pH in the western North Pacific, including Japanese coastal regions. Parameterizations, determined as a function of potential temperature (θ) and dissolved oxygen (DO), provided strong correlations with direct measurements for DIC [the coefficient of determination (R2) = 0.99; the root mean square error (RMSE) = 8

Marine ferromanganese crusts and nodules, which contain a variety of metals, are potential seabed mineral resources. Given their low growth rates, they are regarded as condensed stratigraphic sections that archive millions of years of paleoceanographic information. Ferromanganese crusts and nodules incorporate trace elements like Cu, Zn, Mo, Tl and Ni during growth. The non-traditional isotopic systems

The Kuroshio takes a large meander (LM) path since summer of 2017 for the first time since the 2004–2005 event and is the sixth LM event since 1965. It has been commonly recognized that a cool water pool is distributed broadly in the inshore region between the Kuroshio and southern coast of the Tokai district, Japan, during the LM periods. By using the recently-developed 1-km high-resolution sea surface

We investigated ocean variability at intermediate depths (300–750 m) in the western equatorial Pacific (WEP) using data from underwater sensors of the Triangle Trans-Ocean Buoy Network (TRITON) buoys. The data were specially processed because high accuracy is necessary for such an application, and we confirmed that sufficient accuracy was achieved. Variability of the temperature and salinity was large

The dispersion of Acropora coral sperm is critical for sexual reproduction via external fertilization. Sperm sinking likely plays an important role in the process of dispersion, but its rate of sinking is still unclear. To estimate the sinking speed of coral sperm without turbulence, two experiments were conducted in a water tank filled with 500 L of static seawater in the 0–60 cm layer. In Exp. 1

This study investigated the relationship between phytoplankton biomass and taxonomic composition and hydrographic variables in the Northeastern Tropical Pacific for June 2015, March 2016, and September 2016. Hydrographic data were measured between surface and 100 m; samples were collected at the surface and the deep chlorophyll maximum (DCM) along one or two transects. Pigments were quantified by high-performance