Cobalt rich manganese deposits (CRMD) are frequently discovered on tops and slopes of seamounts in the depths of 800-2,500 m in the equatorial regions of the Pacific Ocean. Because the wireline dredge bucket sampling is not effective to collect crust type samples and to detect buried deposits, the authors have developed a new type gravity corer with a stainless steel core barrel of large bore. A bottom contact camera is also installed as a trigger weight. In the practical uses, the size of the corer is 6 m of total length and 510 kg of total weight. The corer should be dropped freely form a height of 3-6 m above sea bottom. The authors carried out 21 trials on Seamount A, B and C. Results in the experiments were satisfactory. The bottom photos were useful for the recognition of sampling conditions. Maximum thickness of the sampled crust layers was 8 cm. And buried crusts were detected at three locations. In the paper, an outline of the results and some problems are described.
Because Japan is surrounded on all sides by sea, the development of marine life and mineral resources is imperative for its future prosperity. Remotely operated vehicle (ROV) systems are currently used for submarine surveying, but they have a drawback in which they must remain connected to the support ship by a tether cable. We have conducted research towards development a UROV system with an expendable optical fiber cable which overcomes the limitations due to the tether cable while also allowing high-speed signal transmissions. We have constructed two systems. UROV 2000 is prototype system. And UROV 500 is the practical system, which has been developed with improvements on UROV 2000. UROV 500 is used for underwater surveys by Fukui Prefectural Fisheries Experimental Center.
In recent years, ocean bottom seismometers (OBSs) have been used to obtain crustal and upper mantle seismic structures and/or distributions of earthquakes. Most of OBSs used in these experiments are analog recording type. One of the advantages which analog recording OBSs have has been that they can record data continuously for more than two weeks. On the other hand, some disadvantages of analog OBSs can be pointed out; for example, the dynamic range per recording channel is narrow. We have developed a digital recording OBS, which has the same recording length of time as analog OBS's, to obtain higher quality data. The new digital OBS (ORI-OBS) consists of one pressure vessel, an acoustic release system, a transmitter, and a flasher. The pressure vessel (glass sphere) contains sensors, recorder, and battery cells. The design of ORI-OBS except the digital recorder is the same as the up-to-date analog recording OBS. We use a commercial portable digital audio tape (DAT) recorder to store seismic data for long period recording, low power, and low cost. The DAT recorder newly developed has a 16-bit A/D converter and an 8-bit CPU. About 1 GB of data can be stored on a DAT: a continuously recording period is about 12 days on 4 ch at 100 Hz sampling. A real-time clock (RTC) with an accuracy of 5×10-7 controls the timing of the recorder system: the timing of A/D conversion, starting data acquisition at a predetermined time, etc. The electronic setup and monitoring of the recorder, e.g., adjustment of the RTC inside the sealed vessel, can be performed by connecting another computer using the electrical penetrators of the pressure vessel. A 10-second cycle pulse is output to the outside of the pressure vessel to calibrate the RTC. Data on DAT are copied to EXABYTE (8 mm video) tape using the playback system on shore. The EXABYTE system is widely used as a data storage system for UNIX computers. We have used the digital OBS in four experiments, and obtained good quality data from earthquakes, airguns, and explosions.