A method for estimating subsurface density profile in the region surrounding the Kuroshio from surface dynamic height is proposed. We provide a model of the statistical relationship between surface dynamic height relative to 1000-dbar reference level AD (0/1000 dbar) and subsurface density by deriving multiple regression relationships between AD, position (lon gitude and latitude) and amplitudes of the first three modes of empirical orthogonal functions (EOFs) of density profiles. This model is more complete than that proposed by Carnes et al. (1990), who employed the regression relationships between AD and the first two modes of EOFs of temperature profiles. Comparing these models indicates the advantage of applying multiple regression analysis in estimating density profile. The total rms error (consisting of EOF-related and regression-related rms errors) for the multiple regression model reaches a maximum of 0.3 kg m^-3 in August and decreases to a minimum of 0.15 kg m^-3 in February. In every month, the total rms errors in the upper 200 m are larger (0.2 ～ 0.5 kg m^-3) than those in the layer below 200 m where the errors at most standard depths are within 0.2 kg m^-3. Estimating geostrophic current profiles for one section consisting of eight hydrocasts shows the good agreement between geostrophic current profiles calculated from estimated and CTD-derived density profiles (rms difference is 0.04 m s^-1). These results demonstrate the feasibility of estimating density and geostrophic current profiles from AD and position using the modification of the derivation of Carnes et al. (1990).

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We have developed a multi-sensor, salinity/temperature measurement system based on the XCTD (Expendable Conductivity, Temperature & Depth Profiling System) and applied it to an observation well for a groundwater survey in a salt intrusion area. Five CT sensors made by modification of XCTD probes were connected by a cable, and the distances between sensors were adjustable. The cable was 50m long and connected at its end on the ground to a measurement control and data logging system consisting of a notebook computer and peripheral components. In addition, a pressure sensor for measuring fluctuation of water level in the well was included in the system. Observation experiment using this system was carried out in the observation well of the 50m depth in the embankment (about 8.7km upstream from the river mouth) of the River Gonokawa located in the western part of Shimane Prefecture, Japan. We obtained conductivity, salinity, temperature and water-level data every 5 minutes for about two months. By the long-term observation of salinity and water temperature by the CT sensors, it was clarified that the fresh-salt water interface in the groundwater was fluctuating with time. Furthermore, there was a correlation between fluctuation of the ground water level and water-level/flow rate of River Gonokawa.

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With regard to the shipmountedADCP (Acoustic Doppler Current Profiler), which has been widely used for current measurement since 1980's, a type using four acoustic beams transmitted downwardfrom a vessel (four-beamtype) is major internationally. In Japan, however, in addition to the four-beam type, a type using three acousticbeams (three-beamtype) is also popular,but is not well documented in terms of technical issues in comparison with the four-beam type. Although the instrumental principle of the two types does not have big differences, data processing formulations are a little different. The presentstudyprovides a generaldescription of current measurement with three-beam type ADCP, including data processing formulations, error sources, and practical methods of error correction.

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Saline wedge invasion in the Gonokawa River was observed over lengthy periods in summer and winter in 1998. Here we discuss the observed hydrological data from an hydraulic analysis viewpoint. Saline wedge behavior was captured precisely using newly developed observation systems which measured salinity, temperature and identified the interface between fresh and salt water by sonic echo. According to these observations, the length of the saline wedge decreased when the river discharge increased. In other words, the saline wedge moved downstream as the fresh water velocity increased. This showed that the river comprised a two-layer laminar flow with a viscous interface. Wecalculated the length of the saline wedge using specific parameters including depth to the interface, temperature and salinity. The results accorded well with the observed data, and a formula to evaluate the interfacial resistance coefficient incorporating the Keulegan number was proposed. We have also measured the invasion speed of the saline wedge. Simulations were carried out to estimate the invasionspeed, but the results did not agree with the observed phenomena, because the simulation model assumed behavior as a perfect fluid.

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Seasonal variation of carbon of Bacteria, Synechococcus, ANF,HNF,Phyioplankton, and Zooplankton were investigated in Ise Bay, in 1995. In addition, estimated production rates of Bacteria, Synechococcus, phyioplankton, and grazing rates of HNF, zooplankton. Using these results, we approximate production rates of each food chain. In this place, we categorized lOum or less phytoplankton Bacteria Synechococcusand ANF as a producer of Microbial food chain, and cat egorized other producers as a producer of grazing food chain. Then, we compared and examined that interrelationship between each microorganism and environment factor. As a result of this research, water temperature and grazing pressure by HNF were important as change factor of Bacteria, and grazing pressure of HNF and Oikopleura were important as Synechococcus. The microbial food chain/grazing food chain production ratio was 0.66 on the whole, grazing food chain was more important, but microbial food chain was more important in September and December. On the other hand, dominant species of the zooplankton were Penilia avimstris (CLADOCERA), and Bivalve larva and Oithonadavisae (COPEPODA) when produc tion of Bacteria, Synechococcus, etc. was the highest in summer. P. avirostris and Bivalve larva are herbivorous pico- nano, nanoplankton feeder, and O.davisae is omnivorous nano-microplankton feeder. The grazing rates of these dominant species occupied 86% (in August, and the whole 67%) to the grazing rates of the whole zooplankton, and the seasonal variation was similar to change of production rates of Microbial food chain. These results suggest production of a Micro bial food chain links to production of zooplankton. On the other hand, zooplankton population and that species composition were seasonal changing so that food can be used effectively.

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