JAMSTEC’s scientific Drilling Vessel Chikyu is the largest scientific research vessel and introduced the exploration industry riser drilling capability to science research for the first time. Riser drilling allows for ultra-deep drilling below the seabed. Chikyu has the equipment and tools aboard needed to drill deeper into the Earth than any previous scientific drilling vessel. Currently, onshore drilling can sample ancient mantle rocks; however direct sampling of in situ mantle via Chikyu’s cutting-edge research facilities is just coming within reach.
Chikyu is the Japanese platform in support of the International Ocean Discovery Program(IODP) and provides top-class facilities and research into the Earth’s past, present, and future, and is a leading contributor to the advance of human scientific knowledge.
Investigating the ‘Whys’ of Great Earthquakes
Of primary importance is protecting the lives of people living in areas where great earthquakes and tsunamis can occur. In part, Chikyu was built to investigate the mechanisms behind these terrible events, and help us to better understand and therefore mitigate the effects of these natural disasters.
The Nankai Trough off the Kii Peninsula is one such, where the extremely destructive 1944 Tonankai Earthquake occurred. In fact, huge earthquakes have struck this region repeatedly at intervals of about 90-150 years. Chikyu has a drilling project here in the Nankai Trough, and has been able to drill over 3000 meters below the sea floor, a science record depth. During the 2011 JFAST expedition (IODP Exp 343 & 343T), Chikyu was able to drill five holes; sampling the fault zone, the plate boundary, and installed a borehole monitoring system measuring temperature and pressure in water depth of about 6,900 m to about 850 m below the seabed.
Some important scientific findings from these expeditions was that earthquakes could cause slip all the way from the hypocenter to the trench at the front of the accretionary prism, where the continental shelf slopes off as it meets the trench. This is where the subducting oceanic plate dives under the continental plate under, in this case, Japan. Before this expedition, scientists did not believe this could happen. These are only some of the things that ultra-deep water, deep drilling, and riser technology, and operations in harsh conditions and in areas with very strong ocean currents, that are supported by JAMSTEC and MarE3 aboard Chikyu.
The Origin of Life
Life on the primitive Earth first began in a high temperature, high pressure, and anoxic environment. Presently, the only places where these conditions exist are deep underground, in hot springs, and in deep sea hydrothermal vents. Exploration by Chikyu in deep sub-seafloor coalbeds has found assemblages of microbes that have adapted to their environment over millions of years, as it was slowly buried and turned to coal.
These microbes have remained while life on the surface or in the ocean evolved and changed, leaving these assemblages phylogenetically diverged, while much of the genetic material within them are new to science, and not included in any genetic databases.
An important development in this research, are newly developed sample collecting tools that maintain the high, in-situ pressures. Compared to the busy beat of our daily lives, research into, and new developments of the extremely slow-living sub seafloor life can be expected to reveal new advances in microbiological and genetic research.
Quest for the Mantle
Mantle drilling is the plan to drill through the oceanic crust into the currently unexplored mantle of the Earth. through the oceanic crust. This was one of the driving forces for developing and launching the Scientific Drillship Chikyu.
The Earth constantly changes its appearance, due to continental drift and volcanic activity, ever since its creation. The driving force behind this is believed to be the mantle, a strange “flowing solid”. By investigating the mantle, we can clarify how it can effect change on the Earth’s surface.
It’s been more than 50 years since the idea of mantle drilling was first proposed. The scientific targets have also changed and evolved, as “relict mantle” material has been collected, and our fundamental understanding of the mantle itself, has also changed.
Ocean floor drilling studies have shown that the tectonic plates making up the Earth's surface are not all the same. The structure and composition of the different plates vary from place to place, and we still don’t fully understand the global significance of these differences. It is believed that these are closely related to life and the environmental issues.
Chikyu has the capability to reach the mantle, through direct drilling, and collect samples to clarify the essence of the oceanic plate. To do this requires new techniques to drill out 7,000 meters below the seafloor, in regions where ambient temperatures can reach 250 degrees C. Achieving this is a very challenging task, but it has the potential of creating many new advances in technology, tools, and techniques for Japan.
Cores: History Books of the Earth’s Past
Geological samples or core samples, collected from formations drilled by Chikyu are a valuable record of past global environmental change.
For example, researchers aboard Chikyu discovered traces of past earthquakes in core sample, and these can help shed light on past earthquakes and allow for better earthquake mitigation.
To date, Chikyu has collected more than 1,000 cores with a total core recovery length of several kilometers. These cores provide invaluable data regarding past changes and fluctuations in sea level, sea temperature, geomagnetic fields, atmospheric temperature, and more. Careful analysis will reveal the history of the Earth, and provides clues about the future.