Mutsuo Hattori

Implosion of living Nautilus under increased pressure

In a hyperbaric chamber, a living mature specimen of Nautilus pompilius withstood a hydrostatic pressure of 8.05 MPa (80.5 kg/cm 2 ) equivalent to 785 m deep in the sea. Thereafter it was killed instantly by implosion of the shell. Before implosion, the animal reacted physiologically to increasing pressure. Therefore, the depth of 785 m can be assigned the depth limit of N. pompilius. The result bears on critical interpretations on the paleoecology and paleobiology of extinct nautiloids and ammonoids with similar shells.

Late Cenozoic paleobathymetry and paleogeography in the South Fossa-Magna and Enshunada regions, Japan, based on planktic and benthic foraminifera

Abstract Late Cenozoic sequences distributed in the South Fossa-Magna and Enshunada regions are correlated on the basis of planktic biostratigraphy and the paleogeographic evolution of this area is delineated for seven phases (Phases I–VII) based on paleobathymetry estimated from the benthic foraminiferal assemblages. A paleotrench beneath the Kofu Seaway of Oda and Akimoto (1992) , was present during early to middle Middle Miocene time and situated near the boundary between the Eurasia and North American plates. The Misaka paleotrench of Akimoto (1991) , which was located on the boundary between the North American and Paleo-Philippine Sea plates, existed during the early Middle Miocene to Late Miocene, and rapidly shallowed during Pliocene time (CN10). Variations in the paleobathymetry of the forearc basins and bank on the Eurasia plate show that uplift was distributed within a narrow belt (ca. 7 km in width) along the Suruga Trough, and shifted from west to east during Late Pliocene–Early Pleistocene time.

Sea bottom gamma ray measurement by NaI(Tl) scintillation spectrometers installed on manned submersibles, ROV and sea bottom long term observatory

In situ sea bottom gamma ray has been measured using manned submersibles Shinkai2000, Shinkai6500 and the Dolphin-3K rover. The real-time long-term deep-sea floor observatory with gamma ray sensor is under final test before installation on the bottom of Sagami Bay, in depth about 1200 meters. These systems utilize NaI(Tl) scintillation spectrometers of 3 inch in diameter. Three systems that are equipped on manned and unmanned submersibles are operational and a great number of measurements have been carried out around the Japanese islands, North Pacific Ocean, Mid-Atlantic Ridge, Southwest Indian Ocean and Hawaii island. The paper describes the specifications of four systems, the purpose and example of results of measurements.

Environmental Gamma-Ray Observation in Deep Sea

Deep-Sea in-situ radioactivity measurements were initiated in 1964 for investigation of sunken USN atomic power submarine Thresher by using Geiger counters (Wakelin, 1964). Since then, in-situ radioactivity monitoring utilizing a towed-fish and/or remote sea bottom stations has been carried out in various countries. But they are mainly used for surveys of artificial radio activities to evaluate potential risks around atomic power plants, radioactive waste disposal sites and sunken nuclear objects etc. (Jones et al., 1988). Thus, underwater gamma ray measurement has been rather limitedly performed compared to the sub aerial ones, which has been widely utilized for explorations of uranium or other valuable minerals for mining or much wider environmental analysis (Bristow, 1983), due to very effective shielding by seawater. In underwater environment, Yoshida and Tsukahara (1987) reported environmental gamma ray characteristics around an active cold seepage associating with an active fault in Sagami Bay, southern coast of mainland Japan. Besides that, deep-sea gamma ray surveys for scientific use are intensively carried out by ODP-IODP logging for determination of rock types.