The most complicated hydrographic conditions are encountered in the Perturbed Area, where numerous eddies and thermohaline fronts are irregularly distributed between the Kuroshio Extension and Oyashio Fronts at Lat. 38° to 41°N. These features brought the abundance of fishery resources on the northern side of the Kuroshio Extension due to the multiplication of phytoplankton by upwelling. The paleohydrography of the Tohoku Area since 150 ka was reconstructed based on the high-resolution analyses of fossil diatom assemblages in seven cores. Diatom assemblages in the southern margin of the Perturbed Area have been controlled mainly by the Kuroshio and Kuroshio Extension, but in the northern margin they changed in responding to the expansion of the warm-water eddies detached from the Kuroshio Extension and of the southward Oyashio Intrusion. Diatom abundances are higher in the area near shore than in the area off shore, and the diatom assemblages were affected more seriously by the environmental changes in the area near shore. The abundances of extinct diatoms increase in the glacial phase, and diatom abundances and Td' values increase in the interglacial phase. The variation of oceanic diatom abundance is pronounced at 41-kyr and 23-kyr periods, and also Td' values predominating at 60-kyr, 30-kyr, and 23-kyr periods. The seawater mixing during the interval from glacial to interglacial transition induced by orbital-obliquity cycles played an important role in the primary production of oceanic diatoms. The predominant occurrences of extinct diatom species Melosira albicans are accompanied by that of Pseudopodosira elegans throughout the cores.

We explain a method of quality-control (QC) of Argo float positions fixed by Argos system based on checking float speed between the positions considering Argos position errors. The method gives us fairly reasonable QC results which are comparable with those of visual inspection by experts, and several % of position data are identified "bad" in average. This method has been suggested as (one of candidates for) the standard method to International Argo community. An execution program of it was also prepared for Argo community from PARC-JAMSTEC web-site so as that this method is tried widely.

We carried out a wide-angle reflection and refraction experiment using 102 ocean bottom seismographs on a 679-km long seismic line crossing the middle Izu-Ogasawara Arc. The cruise was conducted by R/V Kairei of Japan Agency for Marine-Earth Science and Technology from September to October, 2007. The objectives of the cruise are to reveal the crustal and uppermantle structures across the middle Izu-Ogasawara Arc from Ogasawara Ridge to Shikoku Basin illuminating the structural variations associated with the arc evolution and back-arc openings. In this paper, we summarize the seismic experiment and show the acquired data of ocean bottom seismographs.

Multi-channel seismic reflection (MCS) experiments were carried out in KR07-09 cruise to investigate crustal structures and deformations in the northern Izu-Ogasawara island arc, by using the R/V KAIREI of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Swath bathymetry, geomagnetic, and gravity data are also simultaneously observed during this cruise. Five MCS survey lines (Lines IBr5, IBr9, KT01, KT04, and KT05) with 2001.6km of total line length were obtained in this survey. An airgun array with a total capacity of 12,000 cubic inches (eight airguns with 1,500 cubic inches each) was shot with shot spacing of 50 m, air pressure of 2000 psi, and towing depth of 10 m. These airgun signals are recorded by a 204-channel hydrophone streamer cable with group interval of 25 m. The record length and sampling interval were 18 sec (Lines IBr5 and IBr9) or 15sec (Lines KT01, KT04, and KT05) and 4 msec, respectively. The MCS data has sufficient quality to know the crustal deformation of the arc-backarc transition zone. The preliminary interpretations from the onboard processing result indicated unique features of the basement and sediment in the northern Izu-Ogasawara island arc.

The international project supported by the Integrated Ocean Drilling Program (IODP) started in autumn in 2007 to drill the area off Kii Peninsula, Japan. This area is one of the most active earthquake zones in the world. In the final stage of this project, JAMSTEC plans to install the Long-Term Borehole Monitoring System (LTBMS) in 3.5 km and 6 km riser holes to take a direct look at activities of the plate boundary fault and splay faults above it. As a part of the development of this LTBMS, JAMSTEC started developing an experimental prototype (EXP) of the telemetry system with IODP funding in February 2007. In United States Fiscal Year (USFY) 2007, JAMSTEC defined the operational requirements on the LTBMS and the engineering specifications for its telemetry system with assuming the target hole as 3.5 km riser hole. In the process to define them, JAMSTEC confirmed feasibility of some technical features, such as high speed downhole data transmission, accurate time synchronization between land station and downhole systems, deployment, and so on. This paper describes the operational requirements for the LTBMS and the engineering specifications on the LTBMS telemetry system for NanTroSEIZE 3.5 km riser hole.