We obtained 78 heat flow measurements during 2002-2008 in the area of the Iheya-North hydrothermal field in the middle Okinawa Trough, in order to clarify the spatial extent of the hydrothermal circulation system. Within a small basin surrounded by knolls, three distinct zones are identified with different heat flow values, which we termed the high-, moderate-, and low-heat-flow zones. In the high-heat-flow zone located near the western edge of the basin, extremely high and widely scattered heat flow values (0.01-100 Wm^-2) were measured within ∼500 m of the active hydrothermal mounds, venting black smoker fluid of maximum 311 °C. With increasing distance east of the high-heat-flow zone, heat flow gradually decreases from 1.0 to ∼0.1 Wm^-2 in a region where surface sediment is dominated by clay and a high-resolution bathymetry indicates a smooth seafloor surface. We term this area the moderate-heat-flow zone. Further to the east (∼2 km from the high-heat-flow zone), the seafloor consists of coarser sediment with a rugged surface, and heat flow is very low (<0.1 Wm^-2), as designated the low-heat-flow zone. We suggest that such anomalously low heat flow can be explained by the recharge of seawater into the formation, and that hydrothermal vents or diffuse flow in the high-heat-flow zone can drive this kilometer-scale hydrothermal circulation within the Iheya-North knoll complex, if the sediment below the moderate-heat-flow zone is impermeable enough to prevent vertical fluid migration but is permeable enough to encourage horizontal flow. Although some geological data such as piston core samples, surface morphology and seismic data would support this inference, this hypothesis needs to be tested through more direct evidence and by numerical simulation studies.

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The calculation performance of three types of moment calculation algorithms is evaluated on SX super computer. Those are WorkArray, LISTVEC compile directive, and RETRY algorithms. The used simulation model consists of two dimensional in space. The calculation time of WorkArray and RETRY methods show almost same cost. That of LISTVEC methods is about 1.5 times larger than those of others. The used main memory size of RETRY and LISTVEC methods is almost same cost. That of WorkArray is a few times larger than those of others. The algorithm of WorkArray and LISTVEC are simple but that of RETRY is complicated. However, in the view points of total merits, we recommend to use RETRY algorithm.

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We introduced gamma ray analysis system in order to measure recent sedimentation rates by ²¹⁰Pb method and to obtain dose rates of quartz grains in sediments for optically stimulated luminescence (OSL) dating. Because both ²¹⁰Pb method and OSL dating require precisional values of the radionuclide concentrations, we compared ²¹⁰Pb and ²¹⁴Pb concentrations determined by MCA emulation software of the system, Covell's method and curve fitting method, respectively. ²¹⁰Pb concentrations in some samples determined by the MCA emulation software showed higher values to compare with other methods. The cause would be in an automatic definition of the baseline by the software during the calculation of the net area of ²¹⁰Pb peaks.

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The wide-angle seismic reflection and refraction studies play important roles in determining lithospheric scale seismic structures and understanding tectonic processes in the lithosphere. Recently, a new traveltime analysis method, Jive3D, using flexible model parameterization was developed. We conducted several numerical experiments for evaluating the Jive3D and confirmed Jive3D is a powerful tool for developing lithospheric scale velocity structure models by using wide-angle seismic reflection and refraction data. However, our numerical experiments showed that Jive3D has problems in computational speed and stability for processing large scale wide-angle seismic explorational data. In this study, we improved computational speed and stability of Jive3D. The improved version of Jive3D will enable us to discuss the exact seismic velocity models in the lithosphere.

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Autonomous systems in the open ocean for a long-term observation need components that consume low power. We have been developing a compact drifting buoy system for pCO₂ measurement. The measurement principle for the pCO₂ sensor is based on spectrophotometry. The pCO₂ is calculated from the absorbance of the pH indicator in the solution that is in equilibrium with respect to CO₂ exchange between seawater sample. In general, Xenon lamp or tungsten halogen lamp, which require large amount of power, have been widely used as a light source for a spectrometer. We developed a low power consumption (max: 1.0 W) light source for spectrometry within visible light range by using Light Emitting Diode (LED). The LED light source consists of seven LED lamps (435 nm, 490 nm, 500 nm, 592 nm, 609 nm, 750 nm, White) and output light flux to optical fiber. As the results of stability test and temperature dependency test, the LED light source was stable compared to conventional light sources.

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A supersite has been established and is operated under the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the International Arctic Research Center (IARC) Collaboration Study (JICS), with special emphasis on activities in Research Area 2 (Terrestrial Processes and Variation), which aims understanding multi-scale interactions in the Arctic system, quantifying the impact of observing system components, and utilizing observations in tests and validation experiments for modeling and remote sensing. We have shown that the formation of a supersite under JICS can promote the effective integration of observational studies, modeling, and satellite remote sensing research targeting various components of the processes occurring in the Arctic system. Through the study of these processes, we can enhance our understanding of the nature of the Arctic and the regional aspects of global environmental change, and improve the predictability of climatic fluctuations. We plan to maintain the supersite for the five years of JICS between 2009 JFY and 2013 JFY, as well as to improve the operation of the supersite.

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