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Cold-core (T 27.24 kg/m3 were observed in the near-bottom layer at the shelf break in Peter the Great Bay (PGB) of the Japan/East Sea in March 2010. The anomalously cold water was 0.4 ml/l richer in oxygen than was the surrounding water, and it contained more suspended particles. The observations were carried out by using a moored automatic mobile Aqualog profiler. Profiling occurred as frequent as every hour, allowing us to obtain data with high temporal resolution. The Aqualog profiler delivered vertical profiles of the ocean current velocity, acoustic backscatter at 2 MHz, temperature, and salinity between the depths of 20 and 105 m. Other oceanographic instruments were mounted at fixed depths on the mooring line to measure current velocity, temperature, conductivity, dissolved oxygen, chlorophyll-a fluorescence, and turbidity. Complementary data included ship-borne CTD casts and satellite-borne imagery and scatterometry as well as coastal weather station records. The Regional Ocean Modeling System (ROMS) was employed to study the origin and evolution of the cold water. The model simulated the ocean dynamics at a 600-m horizontal resolution in PGB from 2009 to 2010. The model was forced by the surface momentum, heat and fresh water fluxes of the NCEP-DOE Reanalysis 2. The lateral boundary condition of the model was obtained from nesting into a Japan Coastal Ocean Predictability Experiment model data set. According to the ROMS simulation, the circulation in Ussuri Bay in the northeastern bay of PGB was anticyclonic in February–March 2010. The submesoscale cyclonic vortices generated around the anticyclonic gyre. The submesoscale cyclones tended to move southward out of the bay, and they transported the anomalously cold water towards the outer shelf. As a result, the cold water anomalies were often observed to persist for as long as 2 days near 42.5°N, 132°E. Lagrangian analysis confirmed that this cold water observed by the Aqualog profiler originated in Ussuri Bay. The model simulation showed that the submesoscale cyclonic eddies played a specific role in supplying the densest water from the northern part of PGB to the outer shelf, where the dense water was then entrained by the mesoscale eddies in the Primorye Current zone and could cascade down the continental slope into the deep northern basin of the sea. This transport of the densest water by the submesoscale eddies was estimated to be 5–10·10−3 Sv in February–March 2010.

The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.

Data from the R/V Mirai cruise (May‐June 2000) have been examined to discover how mesoscale processes associated with eddy dynamics directly affect the water masses, the distributions and the vertical fluxes of the dissolved oxygen, nutrients and dissolved inorganic carbon in the western subarctic Pacific. Using maps of the temperature, salinity, dissolved oxygen, nutrients, chlorophyll and sea-air pCO 2 difference we show that the boundaries of the anticyclone eddies in the study region were composed of high productivity coastal Oyashio water. The coastal waters were wrapped around the anticyclone eddies (thus creating a high productivity belt) and intruded inside of them. Using SeaWifs data we demonstrate that temporal variations in the position and the strength of anticyclone eddies advected the Kuril island coastal high productivity waters to the pelagic part, resulting in temporal variations of the chlorophyll in the Oyashio region. Computed vertical fluxes of the dissolved oxygen (DO), inorganic carbon (DIC) and silicate show that the anticyclonic eddies in the Kuroshio-Oyashio Zone are characterized by enhanced vertical fluxes of the DO and DIC between the upper (σ θ = 26.7‐27.0) and lower (σ θ = 27.1‐27.5) intermediate layer, probably due to the intrusions of the Oyashio waters into the eddies.

Based on detailed hydrological and hydrochemical surveys carried out in each of the four seasons of 2008, Amursky Bay in the north west quadrant of the Japan Sea was found to experience seasonal hypoxia. The primary process of hypoxia formation is a microbiological degradation of the ¡§excess¡¨ amount of diatoms under rather low photosynthetic active radiation in bottom layer and weak water dynamics. The microbiological decay of dead diatoms under light deficient conditions intensively consumes dissolved oxygen and produces phosphates, ammonium, silicates, and dissolved inorganic carbon. Existence of a phytoplankton ¡§excess¡¨ is caused by phytoplankton bloom resulting from nutrient pulses into Amursky Bay. There are two main sources of these nutrients: the waste waters of Vladivostok city and discharge from Razdolnaya River. The river delivers more than two times the amount of nutrients than the waste waters of Vladivostok. It is suggested that the phytoplankton ¡§excess¡¨ might be caused by an enhanced supply of nutrients delivered into the surface layer resulting from the increased discharge of the river on a short time scale. Our data suggest that hypoxia is seasonal, with a peak at the end of summer. The upwelling of the Japan Sea water in the beginning of the fall season and its advection across the shelf is the primary process by which the hypoxia is destroyed. During the winter, strong vertical mixing due to termohaline convection makes the water column uniform and brings more oxygen into the water along with high primary production under the ice. Thus, during the winter season, the ecosystem of Amursky Bay recovers completely.