The Soya Warm Current（SWC）flows through a shallow strait between the Japan Sea and the Sea of Okhotsk. A surface cold belt with a subsurface doming structure forms offshore of the SWC axis. Mechanisms of the cold belt formation are discussed from a point of view of resonant interaction between a barotropic stratified flow and a shallow sill, and subsequent baroclinic adjustment along SWC. When a stratified current rides a slope upstream, the thermocline displaces upward greatly and outcrops owing to resonant generation of internal Kelvin waves if the upper layer is thinner than the lower layer. These upwelling features closely resemble those along the southwestern coast of the Sakhalin Island. SWC then flips from an upwelling-type to a downwelling-type structure, in doing so it transits from the west coast of Sakhalin to the east coast of Hokkaido. It is thistransition that leads to the offshore doming structure, which propagates downstream as a vorticity wave, manifesting the cold belt at surface.

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In the vicinity of the coastal area of the Okhotsk Sea an oceanographic survey was conducted to elucidate the relationship between oceanographic structure and primary productivity in２００３and２００４. Soya Warm Water（SWW）was found near the coast of Hokkaido during spring and summer. Okhotsk Surface Low Salinity Water（OSLSW）and Intermediate Cold Water（ICW）were present at the offshore surface and at mid-depth, respectively. Nutrient concentration was the highest in ICW at around ２０ μM of nitrate and low in SWW and OSLSW. Nutrient rich ICW showed a low chlorophyll a（Chl a）concentration. Incubation experiments were conducted to examine the effect of water mass mixing on primary productivity. No increase in Chl a and a decrease in nutrients was observed during a week-incubation in the bottles of individual seawater. However, the mixing of OSLSW and ICW, and SWW and ICW showed an increase in Chl a and a decrease in nutrients. A large increase in＞１０μm size Chl a was observed in the latter case. Diatom seemed to be the dominant phytoplankton because silicate also decreased in the bottle. The reason for this rapid growth of diatoms might be the supply of dissolved Fe from SWW because dissolved Fe was the highest in this water mass at more than２nM. This result explains the persistence of a high Chl a zone near the boundary between SWW and ICW during spring and summer. Furthermore, we examined the relationship between oceanographic structure and diet supply for scallop culture on the seafloor under SWW. There was a tendency of higher growth of scallops during April and June when ICW approached near the farming ground of scallops. This approach of ICW supplied nutrients to SWW, accelerating phytoplankton production, especially large diatoms and as a consequence led to the good growth of scallops.

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Motivated by the saying of scallop farmers working in Saroma-ko lagoon that the growth rate of scallops is higher in years with more stormy days than in less stormy years, we performed a temporal observation in１９９８at a single station. The physical／chemical conditions and particulate matters in the water column were examined to confirm the appearance of the resuspension and upward transport of sediment surface organic matter as the food of the cultivated scallops. The observed data were as follows : １）the water column became more uniform coincidently with storms, ２）particulate matter, especially particulate sulfur formed in／near the sediment and diatoms increased with storms, ３）most of the increased diatoms cells were benthic and dead ones, ４）living benthic diatom cells appeared during storms and the day after. These facts demonstrate clearly the resuspension and upward transport of particulate organic matter from the sediment in Saroma-ko lagoon to the depths where the scallops are cultivated.

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Occurrence mechanism, characteristic distribution and impact on low trophic level of hypoxic water in Lake Notoro, Hokkaido were investigated using data from July to September ２００７‐２００９. The stratification of the water column might be important for the occurrence of hypoxic water. The hypoxic water was observed at the bottom from the center to the most inner part of the Lake, implying that wind-driven current by the southerly wind is important for the hypoxic water distribution. The increase of nutrients was observed with the decrease of dissolved oxygen. Surface chlorophyll was the lowest in ２００７, when wind speed was the lowest in the three year. These results indicate the vertical mixing induced by wind might be important for nutrients supply to surface layer. In conclusion, low trophic level after summer in Lake Notoro might be affected by nutrients supply with the occurrence of hypoxic water and the vertical mixing induced by wind.

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Size-fractionated chlorophyll a and primary productivity were measured in the coastal area of the Shiretoko Peninsula in May to June（late spring to early summer）and in August and Septembe（r late summer to early autumn），２００７－２００９．In the late spring to early summer, large size phytoplankton（＞１０μm）contributed to total chlorophyll a concentration in the Okhotsk Sea side of the Shiretoko Peninsula（western side），whereas small size phytoplankton（＜２μm）were more common in the Nemuro Straight side of the peninsula（eastern side）．In contrast, maximum chlorophyll a-specific primary productivity（an index of phytoplankton growth rate）was observed in the large size phytoplankton on the western side, and large or middle（２－１０μm）sized phytoplankton were found on the eastern side, implying that they are important primary producers．In the late summer and early autumn, the large size phytoplankton contributed to total chlorophyll a concentration on the western side, whereas large or small size phytoplankton were found on the eastern side．However, maximum chlorophyll a-specific primary productivity was observed in the middle size phytoplankton on the western and eastern sides, implying that they are important primary producers．The results suggest that important primary producers are not different between both sides of the peninsula, but change seasonally．

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To recognize oceanographic ecology in the Nemuro Bay and to improve the timing of release of juvenile chum salmon （Oncorhynchus keta）, observation cruises were operated from ２００７ to ２００９. Sea surface temperature in coastal region rose to prefer temperatures, ８－１３℃, in late May in２００７and２００９, and in early June in２００８. Prefer temperature was maintained over ５０days in２００９, but３０or４０days in２００７and２００８, respectively. Temperature difference between Nishibetsu River and coastal region of Nemuro Bay exceeded ９℃ in early May in ２００８, since riverine water temperature changed simultaneously with air temperature, while warming of coastal area was delayed. Sea surface salinity, on the other hand, was freshened lower than３１ in coastal area, and its distribution pattern differed among three years studied. Numerical model, which was employed to examine current field of Nemuro Bay, suggested that low salinity water distribution was affected not only by river flow rate, but also by wind. Particle tracking experiment reproduced juvenile salmon distribution in coastal area, and it showed that juvenile chum salmon moved passively with oceanic current. As sea surface temperature, a conventional factor of early ocean life of juvenile chum salmon, sea surface salinity and surface current field were also important to consider species of zooplankton and migration pass of juvenile chum salmon in Nemuro Bay.

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We investigated the quality of water of the inflow river in Lake Furen from May, ２００６ through November, ２００８．The mixed form of river water and the seawater in Lake Furen changed by ebb and flood tides and was weak mixed type of the estuary circulation at the time of the ebb tide and was strong mixed type at the time of the high tide．Highly concentrated nutrients from dairy farming drainage flowed into Lake Furen, and we examined the amount of nutrients used by phytoplankton in the estuary． We calculated the data from April, ２００７ to March, ２００８，which was ５２９ton in DIN and ５８ ton in DIP when we estimated load quantity in the year to Lake Furen by３main rivers, using the mean flow quantity as a minute for one year．Furthermore, this value became２，５３３～４，５５０ton C when the amount of phytoplankton primary production using inputted nutrients was assumed to be ５４－９８％ in DIN case, and approximately １００％ in DIP case when we assumed only inputted nutrients from the river．In addition, the particles produced in the lake tended to not flow easily outside the lake．In addition, we estimated the silt content of the sediment outer layer at various depths, and we revealed that the particles of the water column were selectively deposited as the silt became higher at inner part of the lake．

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We determined biogenic silica（BSi）content and estimated the Si budget within surface sediments（０－１０mm）of the eastern Seto Inland Sea, Japan, together with total organic carbon（TOC）, total nitrogen（TN）and total phosphorus（TP）. The BSi content determined by the DeMaster's technique ranged between２．０２and２４．８mg Si g－１, with a mean（±S. D.）value of１１．６ ± ７．４mg Si g－１（n＝２５）. The horizontal distribution of BSi in the area was related to that of TOC, TN and TP, and significantly correlated with the water content in the sediment（r＝０．８７５）. This indicates that the level of BSi content is influenced by the sediment characteristics, and the horizontal distribution of BSi reflects the re-distribution of fine particles as a result of hydrodynamic processes, as well as the amount of the phytoplankton in the overlying water column. The deposition rate of BSi, TOC, TN and TP from the water column to the surface sediment through biological activities in Osaka Bay-Harima Nada Area, a major part of the eastern Seto Inland Sea, is estimated to be １０．３×１０４t Si yr－１, １１．７×１０４t C yr－１, １．４１×１０４t N yr－１ and０．２６×１０４t P yr－１, respectively. It was also found that the accumulation rate of BSi, TOC, TN and TP in the surface sediments accounts for ２８％, ７．２％, ４．９％ and ６．７％ of Si, C, N and P production by phytoplankton in the same area, respectively. These results suggest that most particulate carbon, nitrogen and phosphorus produced by phytoplankton in the eastern Seto Inland Sea is transported to the outer area through water exchange whereas, in the case of particulate silica, sediment acts as a major sink.

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In Kagawa Prefecture, the suspended organic matter concentration（phytoplankton origin）was high in waters dammed by the river mouth weir. The supply and circulation of organic matter from the river to the coastal area of the Seto inland sea were studied using δ１３C and δ１５N. The contribution rates of river-derived organic matter, and that produced in tidal flats and from the sea were １４－５７％, ４－６２％ and １－６７％ in order. Organic matter produced in the tidal flats was used by benthos in the tidal flats, however, river-derived organic matter was not used. It was shown that organic matter carried from the polluted river was a major fraction of the organic matter in the tidal flats ; however, it was not sufficiently utilized by the tidal flats. It was also considered that river- and tidal flats-derived organic matter directly entered the coastal sea downstream, around Kagawa Prefecture.

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The relationship between dissolved oxygen（DO）near the sea floor and acid-volatile sulfide（AVS）in surface sediment in Funka Bay was investigated seasonally during ２００７ to ２００８. DO showed an annual cycle（low in autumn, high in spring）, but AVS varied over a shorter time-scale of several months. To qualitatively examine the relationship between DO and AVS, a simple analytical Box-model with two parameters（constant reduction and variable oxidation）was used. Model results suggest that  AVS rapidly increases and decreases in response to the sinusoidal DO-forcing,  the maximum phase of AVS lags ０°－９０° behind the minimum phase of DO, and  the amplitude of AVS is smaller when the oxidation-reduction rate decreases．These properties can explain the AVS variation over a one-year cycle. Abrupt decreases of AVS over shorter periods were caused by disturbances with one-order higher oxidation than the ordinal situation, but physical or biological causes for such disturbances could not be detected．

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