Marine Ecosystems Research Department - jamstec japan agency ...

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
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