Chimney and mound samples collected by "Shinkai 6500" from two hydrothermal vent fields in the Mariana Trough were studied mineralogically and geochemically. One of hydrothermal vent fields is so called Forecast Vent Field at the depth of 1,450 m in the South Mariana Trough, and another deeper field is so called Alice Spring Field at the depth of 3,600 m in the Middle (or Central) Mariana Trough. Ore and gangue minerals from the both hydrothermal fields are similar, but the quantity of them is different in each field. Main ore minerals in the South Mariana Trough are sphalerite, marcasite, chalcopyrite and tetrahedrite-tennantite, and those in the Middle Mariana Trough are wurtzite, chalcopyrite and tetrahedrite-tennantite. As gangue minerals, gypsum is abundant and barite is poor in the South Mariana Trough, but, in contrast, anhydrite and barite are rich in the Middle Mariana Trough. Chemical compositions of ore minerals are analyzed by EPMA. Sphalerie contains FeS up to 2.5 mol %.

The trapping temperature of fluid, i.e. formation temperature is obtained after pressure correction for the measured homogenization temperature of fluid inclusion. Pressure-corrected trapping temperature of fluid inclusion in wurtzite and anhydrite in the South Mariana Trough averages 240℃, and that in wurtzite in the Middle Mariana Trough averages 278℃. The measured maximum temperatures during this survey are 210℃ and 267℃ in the South Mariana Trough and Middle Mariana Trough, respectively. The salinity of fluid is determined from melting temperature depression of fluid inclusion.

Sulfur isotopes of sulfide and sulfate minerals are examined, and bulk chemical compositions of chimneys are analyzed. It is noteworthy that some chimneys contain gold of the order of 10 to 30 ppm.

The Kuroshima Knoll, located in the southwestern part of the Ryukyu Arc, is one of the best fields for the study of gas hydrate dissociation, because the Pressure-Temperature condition at the top of the knoll is close to the phase boundary between gas and hydrate. In order to understand the geothermal structure around the Kuroshima Knoll, heat flow and thermal conductivity measurements were carried out around the knoll during the R/V "Kaiyo" KY03-09 Cruise. During heat flow measurements we found that the vertical variation of water temperature was as large as 1.2 degC just above the seafloor at Sites A and B on top of the knoll. This can either be temporal or spatial variation, and it disturbs the subbottom temperature field significantly, possibly affecting the state of hydrate. The heat flow value is 42 mW/m² and thermal conductivity is 1.0 W/m/K at the Site 2 in the Yaeyama Basin. The thermal conductivity value in the Yaeyama Basin istypical for the ordinary marine sediment. On the other hand, the thermal conductivity is much higher (1.8 Wm^-1K^-1) at the Calyptogena colony site (Site A) on top of the knoll.

We carried out a deep wide-angle seismic experiment using a large airgun array and total 103 ocean bottom seismographs (OBSs) in the northern Izu-Ogasawara arc area, which was conducted by R/V Kaiyo of Japan Agency for Marine-Earth Science and Technology (JAMSTEC) from July 8, 2004 to July 22 (KY04-08 cruise). Objectives of this cruise are to know a velocity structure of the arc-arc collision zone and to understand relationship between the crustal growth and the arc collision, which is one of important parameters to clarify nature of the oceanic arc growth. An airgun-OBS seismic line was set from western Sagami Bay near granitic Izu peninsula to Tori-shima along the direction of the volcanic front. We shot a large airgun array with total volume 12,000 cu. in. and recorded the seismic signals on OBSs with four components and a hydrophone streamer. In this paper, we summarize information of the seismic experiments and introduce OBS data and reflection data.

Dual-Doppler radar system is a unique instrument to detect the three-dimensional structure of cloud systems including the rain particle distribution and their movement. In the real observation of cloud systems using dual-Doppler radars, researchers have to choose a variety of options, such as time of collecting three-dimensional volumes or intervals of antenna scans, depend on their altitude, their speed of propagation, and their development activity. All the options are not satisfied, the tradeoff for high spatial resolution is lower time resolutions. Researchers have to determine the options before observation, however, it is difficult to know the effect of the tradeoff for the options they made. To know the better options before the observation, an idealized dual-Doppler observation is made using the numerically simulated cloud systems developed in the same location for observation targets. This documents introduces the process of finding better options on the observation of tropical cloud systems in the western Pacific Ocean.

Spatial distribution of the Argo floats in the Southern Ocean was simulated based on an output of a high resolution ocean general circulation model.

Giving initial uniform distribution of the floats, numerical simulations were performed for the parking depths of 2000 m and 1000 m, respectively, with and without sea ice. When the sea ice was ignored, the floats were distributed almost uniformly even four years later but generally showed northward shift. Under sea ice condition, most of the floats were lost south of 62°S one year after the float deployment while most of the floats survived north of 53°S if the sea ice concentration was considered as the survival rate of the float in the corresponding region.

A property change of strain gauges type pressure sensor installed on TRITON buoys was investigated for correction of pressure and salinity data. Output data from pressure sensors on deck after recovery indicated overestimated value as a result of hysteresis of pressure sensor. A value of overestimate surpasses 10 dbar in the most remarkable case, and it becomes an error of 0.005 psu by salinity conversion. It is critical for our aim of salinity measurement accuracy (0.02 psu). Moreover, sensor calibration data reveals larger influence of hysteresis under actual high-pressure condition. It is also obvious that hysteresis occurs at a stage put in high-pressure installed depth, at least 10 days mooring, and its value is different among each sensor. This result suggests that removal of a bias, which corresponds to hysteresis induced by calibration data, become effective.

The hydrographic history of the Kuroshio-Kuroshio Extension system east off Honshu during 200 thousand years was reconstructed based on high-resolution records of fossil diatoms in three cores recovered from the area beneath the Kuroshio Warm Core. The influences of the terrestrial environments are implicated in the fluctuations in number of diatom valves, and in relative abundances of extinct, freshwater and littoral diatom species; in the Kuroshio Extension off shore area extinct, freshwater and littoral diatoms showed decrease in their relative abundance. The Earth's orbital parameters and the variations in isostatic balance in the Northern Hemisphere are considered to have controlled the species composition of diatom flora. The warm-water diatom species in littoral-neritic association are predominant in the near shore area due to the Kuroshio flowing northeast along the coast of southwest Japan. The cold-water species of oceanic association are predominant in the Kuroshio Extension off shore, where southward Oyashio flows in from the Bering and Okhotsk Seas.

Surface water samples were collected from a site TP03 in the Tsugaru Strait during March-September 2003. Cell density and species composition of living coccolithophorids in these samples were studied under a scanning electron microscope (SEM). The cell density maximum was shown in September 2003, which corresponded to a high sea surface temperature. A total of fourteen coccolithophorid species were recognized. Seasonally, the coccolithophorid assemblages in spring and early summer were dominated by Gephyrocapsa oceanica, whereas the assemblage in late summer was dominated by Emiliania huxleyi.

For the better understanding of carbon cycle in the northwestern North Pacific where rough sea condition frequently refuses oceanographic observation by research vessel, time-series observation for the biogeochemistry with mooring system has been requested strongly. Mutsu Institute for Oceanography (MIO) challenged to deploy the mooring system that is anchored on the sea floor at > 5,000 m depth and its top with automatic instruments is located in the euphotic layer, upper 30–50 m. In order to enable this deployment, behaviors of mooring system such as tilt and depth for instruments during deployment and observation were simulated, and precise lengths of wire and nylon ropes used for mooring systems were measured under the mooring tension on land. Based on these procedures, two types mooring systems were deployed at stations K-1 (51°N, 165°E) and K-3 (39°N, 160°E) in October 2002 and recovered in November 2003. Mooring systems were successfully deployed within 300 m from a "target" points and depths of top of mooring systems could be located between 40–60 m for K-1 mooring and 50–70 m for K-3 mooring as we designed except high current period.

In the coring operation carried out in science drilling or oil / gas exploration, core samples should be recovered without being contaminated to preserve the conditions at drilled point. Therefore, development of a coring system, which reduces a core contamination caused by contact with drilling fluid as much as possible, has been strongly required. In this research, a coring system, which can coat the core surface with gel having physical/chemical characteristics with the progress of coring, was developed. After the fabrication of prototype system, the fundamental functions and the reduction effect of core contamination were confirmed by on-land drilling test using it.