Marine Ecosystems Research Department - jamstec japan agency ...

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Japan Marine Science and Technology Center Research Activities Deep Sea Research Department Overview The research activities at Deep Sea Research Department are focused on better understanding of the earth's dynamics operating in deep oceans with emphasis on active geological, geophysical, and geochemical processes evident at and/or through the ocean floor. These processes comprise important aspects of the whole earth dynamics because most of the plate boundaries exist beneath deep waters, where plate deformations are concentrated and energy and material fluxes are pronounced. Our strategy is to take a multi-disciplinary approach in order to identify and to solve problems related to these processes. We consider close access to these processes to scrutinize them to be most important. Thus, we try to make the best use of and improve the facilities available at JAMSTEC including manned and unmanned submersibles. In particular, significant efforts are put into establishment of seafloor observatories to detect and monitor active geological processes and investigate their significance. Our department has been conducting two major projects and related studies focusing on these, which are () Ocean Floor Geodynamics, and () Observation Networks on Deep Sea Floor. The research highlights during FY (April to March ) are; () we have concluded our surveys around the Hawaiian volcanoes to construct a model of the growth history and landslides of these volcanoes. () Seismo-electromagnetic surveys of the Mariana Arc-Back Arc system in collaboration with U.S. groups have entered the second year. () Significant improvements were made to the data management system of the cabled observatories. New staff members at DSRD during this period are Natsue Abe (petrologist), Tetsuro Hirono (geologist), Weiren Lin (physical properties specialist), Hiroyuki Matsumoto (earthquake engineer). Eiichi Kikawa (paleomagnetist) returned from Washington Office. A brief summary of our seafaring activities is attached at the end of this report. Detailed scientific results are being published in outside review journals and JAMSTEC reports. During FY, our staff members and fellows were authors of peer reviewed outside journals. 1. Ocean Floor Geodynamics a) Gas bubbling site at Kuroshima Knoll at the forearc of Ryukyu Arc The role of gas hydrates as reservoir of carbon needs to be quantified in order to understand its effect to the global change. Around Japan, we have designated Nankai Trough area, Sagami Bay area and the Kuroshima Knoll site as sites for quantifying methane seepage. Since the discovery of the clam community at the Kuroshima Knoll in , we have found that the site is one of the few discovered areas in the world of active fluid venting including gas bubbling. Here, more than gas bubbling spots were found surrounded by Bathymodiolus colonies, and carbonate rocks were formed by cold seeps containing methane gas. Recently obtained reflection seismic records show polarity reversal indicating fluid inclusion at about m depth below the vents, which suggests gas storage and pathway along the well-developed faults (Fig. ). In order to quantify this flow, we deployed CAT (Chemical and Aqueous Transport) meters jointly with Scripps Institution of Oceanography, thermometers, a CTD, and a current meter. These instruments were recovered after to months of observations. b) Hawaii Volcanoes studied by Shinkai 6500 The manned submersible Shinkai made dives south of Hawaii Island and around Oahu during July-September, as the final phase of the Hawaii project that started from (Figure ). The survey was a multi-institutional effort led by E. Takahashi (Tokyo Inst. Technology) in order to clarify the volcano growth history, ridges extending from volcanoes, and volcanisms at the edge of the plume head. Hawaiian volcanoes are known to accompany large landslides as part of their growth history. During this survey, the 19
JAMSTEC 2002 Annual Report Deep Sea Research Department (a) (b) Time (ms) 700 710 720 730 740 750 760 770 780 790 800 810 820 830 840 850 860 870 880 890 900 910 920 930 940 950 960 970 980 990 1000 1010 1020 1030 1040 1050 1060 1070 1080 1090 1100 1110 1120 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 700 710 720 730 740 750 760 770 780 790 800 810 820 830 840 850 860 870 880 890 900 910 920 930 940 950 960 970 980 990 1000 1010 1020 1030 1040 1050 1060 1070 1080 1090 1100 1110 1120 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 Calyptogena colony carbonate crust Fig. 1 (a) A single-channel seismic profile on the top of the Kuroshima Knoll. Reverse polarity and lowvelocity zone are recognized beneath the methane seep sites. Blue lines and brown lines are interpreted as faults and layer boundaries, respectively. Inset shows the area map of the Kuroshima Knoll. (b) A CAT meter installed on a Calyptogena colony. gathered data included geological data regarding the landslide from Mauna Loa. An intensive survey of submarine ridges formed by magma intrusions was made along the Hana Ridge (Haleakala east rift zone) extending km from the Haleakala volcano of Maui as well as at Puna Ridge from Kilauea and at Hilo Ridge from Mauna Kea. The change in chemical components of the magma bodies among the volcanoes and the ridges suggests that the magma source changes as the volcano passes over the plume. and passive sources (airguns and earthquakes). R/V M. Ewing surveyed the area around ˚N using MCS and OBS for crustal scale investigation. R/V Kaiyo employed OBSs to shoot a transect along ˚N 25 00' 24 30' 24 00' 23 30' 23 00' 22 30' 22 00' 21 30' c) Seismo-electromagnetic surveys of the Mariana Arc system The Izu-Ogasawara-Mariana arc system is an oceanic arc system extending more than km from central Japan southward forming the eastern edge of the Philippine Sea. The structure of the trench-arc-backarc system provides important information about the formation and evolution history of the system as well as its dynamics and mass and energy transfer budgets. Among various cruises made to the area for marine geological and geophysical investigations, we highlight the ongoing Japan-U.S. collaborative study using multi-channel seismics and ocean bottom seismographs (short period and wide-band types) for active 21 00' 20 30' 20 00' 19 30' 19 00' 18 30' 18 00' 17 30' 17 00' 200 00' 201 00' 202 00' 203 00' 204 00' 205 00' 206 00' 207 00' -5000 -4000 -3000 -2000 -1000 -6000 -5500 -4500 -3500 -2500 -1500 -500 BATHYMETRY Fig. 2 Bathymetric map in the underwater area of the Hawaiian Island. JAMSTEC leads a four-year (1998, 1999, 2001, and 2003) Japan-USA collaborative survey of the underwater flank of the Hawaiian volcanoes. This exploration utilized manned and un-manned submersibles, dredge and pistoncorer to sample, and ship-based sonar systems to map the bathymetry from the seafloor. The resulting swaths reveal the seafloor in stunning detail. m 20
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