We reinvestigated tephra and cryptotephra stratigraphy of the Late Pleistocene deep-sea C9001C cores collected during the D/V Chikyu shakedown cruise. We identified 26 glass shard concentration horizons (spikes) corresponding to four previously reported tephras (G1, G2, G3, and G4 from top to bottom). We newly found three visible tephras and 19 nonvisible cryptotephras (G0.0-0.9, G1.1-1.4, G2.1-2.5, and G3.1-3.3). We newly correlated spike G0.2 with the Towada-Hachinohe (To-H: MIS 1/2, 15 ka), G0.5 with the Towada-Biscuit 2 (To-BP2: MIS 2, 18 ka), G1.1 with the Komagatake-i (39 ka), G1.2 with the Kutcharo-Shoro (MIS 3, 40 ka), and G3.3 with the Sambe-Kisuki (MIS 5c, 100 ka) tephras. Spikes G2.2, G2.3, and G2.4 may correlate with the Towada tephra series (seven correlative candidates), spike G3.1 with an Ontake volcano tephra (MIS 5b-5c), and spike G3.2 with the Towada-Castera or Towada-Aosuji (both MIS 5b-5d) tephra. We classified spike G0.1 as reworked materials of the underlying spike G0.2 (To-H), and the combinations of spikes G0.3 and G0.4 and of G0.8 and G0.9 as the result of repeated reworking of the underlying spikes G0.5 (To-BP2) and G1 (To-Of), respectively. We also classified spikes G1.3 and G1.4 as reworked mixtures of Shikotsu-1 tephra with glass shards from other tephras. The upward decrease of the glass shard populations above spikes G3 and G4 is interpreted as indicating immediate reworking of the tephras after initial emplacement. Whether or not a marine tephra is preserved depends on depositional and post-depositional processes and not simply on the eruptive volume or the distance from source. Nevertheless, cryptotephras recognized by glass shard concentration horizons in marine cores can provide additional datum planes and contribute to marine tephrostratigraphy.

Cable-based observation system is suitable tool for continuous ocean monitoring. Because cables can supply the power and realize high capacity data communication, such cable-based ocean observation systems have been widely used. However, general cable-based observation systems are deployed on flat and normal temperature seabed to prevent physical and heat damages to the cables. Therefore, there are no information on construction method of cable-based observation system for seafloor hydrothermal activities. How to design such types of the cable system, what types of parameters should be surveyed beforehand, are not established. In this paper, the authors propose the designing method for cable-based observation system constructing on seafloor of active hydrothermal vent field. The in situ application of techniques consisted of the method were examined on hydrothermal environment through the research cruises by using remotely operated vehicle (ROV). The practicality of GIS based data management system constructed for long-term survey of seafloor condition and secure of observation system, were investigate by using data collected in the cruises. The possibility of the cable-based observation system is discussed in this paper.

High performance CTD sensor for mooring system and profile measurement was developed. Circuit performance for realizing the target resolution (water temperature 0.0001 degC, conductivity 0.00001 S/m) was obtained by developing sensor signal processing method and circuit configuration. We developed a thermistor probe which has low depth dependence and a response time sufficiently short for profiling measurements. We also developed a conductivity sensor device of platinum electrode with high performance and repeatability. The new sensors have been calibrated and repeatedly tested in situ ((m-)TRITON buoy measurement and CTD castings) to improve the quality. As a result, the target performance (initial precision 0.002 degC, 0.0003 S/m, and time drift characteristics to withstand long-term mooring) comparable to SBE sensor (SBE37), was obtained.

We conducted geophysical observations on the Ontong Java Plateau (OJP) and its vicinity from late 2014 to early 2017 to determine the underlying crust and upper mantle structure beneath the OJP. Most of the OJP was emplaced in the present South Pacific region at 122 Ma by massive volcanism, but the origin of this volcanism are still debated. Previous studies have suggested that seismic velocity beneath the OJP is anomalously slow, thus this could represent thermal or chemical remnants of the volcanism. However, the seismic resolution of the slow anomalies is poor due to lack of seafloor observations. The observation network named “the OJP array” is composed of seafloor and island stations. The seafloor stations have broadband ocean bottom seismographs and ocean bottom electromagnetometers. The island stations have broadband seismographs. The OJP array is designed to obtain seismic and electrical conductivity structures of the mantle beneath the OJP with better resolution than that of previous studies. Joint analysis and interpretation of seismological and electromagnetic data should provide tight constraints to thermal and chemical structures and clarify the origin of OJP emplacement.

Restriction to marine observational data disclosure at governmental research organizations with disciplines similar to JAMSTEC's in the United States of America, Canada, French Republic, and the United Kingdom are surveyed. Here, the question is whether there are any kinds of data are not necessarily to be disclosed regardless of the recent current of data disclosure. In these states, national securities, privacy, and commercial confidentiality are qualified for exemptions.

Vesicomyid clams, including the genus Phreagena, are dominant members of various deep-sea chemosynthesis-based animal communities. They harbor symbiotic sulfur-oxidizing bacteria in the epithelial cells of their gill tissue, and the bacteria are transmitted to the next generations via eggs. We created a monoclonal antibody (mAb) library against the gill of P. okutanii and observed mAb CokG-D1D3 to react to the symbiotic bacteria and three mAbs (CokG-Y1F7, CokG-J10D2, and CokG-J3G4) to bind to hemocytes of P. okutanii. The signals of mAb CokG-D1D3 were localized in the epithelial gill cells called bacteriocytes. We also observed a small number of clear signals of the antibody in the epithelial follicular cells of the ovary. The signals of mAb CokG-D1D3 almost exactly overlapped those of the anti-E. coli GroEL polyclonal antibody, while, in the gill, the signal areas of the latter seemed to be slightly wider than those of the former. Among the three mAbs against the hemocytes, mAbs CokG-Y1F7 and CokG-J10D2 reacted to a large fraction of the hemocyte populations, but mAb CokG-J3G4 reacted to a smaller fraction. mAb CokG-Y1F7 was observed to bind to the hemocytes distributed widely in the interstitial spaces of various tissues. These monoclonal antibodies are expected to be useful for studying the interactions between symbiotic bacteria and host cells and the distribution and functions of hemocytes in deep-sea vesicomyid clams.

Portable multi-channel seismic reflection (P-MCS) system of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) was implemented in 2011. The constant travel-time noises have been appeared on the seismic shot gather of this P-MCS system since its implementation. The noises have been recorded on several active sections of the streamer cable, randomly. Although it is inferred that the constant travel-time noise is caused by the electrical property of the streamer cable, it doesn't lead to fundamental solution currently. The constant travel-time noises have similar frequency and higher amplitude to the seismic reflection signals. Therefore, these noises remain on the stacked data, and overwrite reflection signals. In order to suppress the constant travel-time noise effect, it is necessary to attenuate only the noise, which distinguished from the seismic reflection signals. Here, we attempt to attenuate the constant travel-time noise, and show that the application of the F-K filter (frequency-wave number filter) can attenuate the constant travel-time noise on the seismic shot gather.