Please refer to CDEX's website.
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In May 2001, the Declaration to promote Integrated Ocean Drilling Program (IODP) called eInitial Science Plan (ISP)f was introduced with specific research goals for the coming ten years. This guideline was established by many scientists from all over the world, thought and debated through by considering a little bit the intentions of the funding agencies as well. Therefore, this guideline is an important principle for all who are involved in this program.

(Above) The cover of ISP booklet
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Following are the most important research topics of IODP to be investigated.

• The Deep Biosphere and the Subseafloor Ocean
• Environmental Change, Processes and Effects
• Solid Earth Cycles and Geodynamics

We are in the year 2010, and we have three years to go before the end of the first term of this program; however, have we made great progress to attain these goals? We can call these goals as our ideal destination which we intend to solve, but honestly speaking, we have not clarified these much and the goals are still hazy in the distance. I confess that it is actually invisible. Especially, for the target ginvestigation of the subseafloor biosphereh, almost no microbiology-dedicated drilling expedition was made since the last ODP Leg#201 expedition in 2001. This is not good. We need to make actions.
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On the other hand, there has been a great scientific progress in the subseafloor biosphere in the past decade by using samples collected from the ODP expeditions. Thus, we do have some brandnew ideas of how the biosphere is present and functioning in the subseafloor. In the past, as in 1998, scientists used to be interested in the largest biomass potential of the subseafloor in the Earth as it was showed by Whitmanfs calculation. However, the latest researches show that the prediction may be incorrect; there can be a large biosphere, but not the glargesth one. Moreover, there is a fact that we have been examining only the very thin layer of the ocean crust, which is the gsedimentary biosphereh, hosting microorganisms. What we are now conscious of from the new results are: the subseafloor biosphere is not the gdead worldh without any living organism, but the almost-undetectably slow-living, -breathing and -fermenting; most of the microorganisms in the dark subseafloor are likely on the fallen leftover photosynthetic products made on the surface of the Earth; the Achaea (one of the prokaryotic domains) which were thought to be the minorities in most of the Earthfs habitable environments might be the majority in the subseafloor sediments. Such results lead us to understand more about the biosphere under the oceanfloors.

(Above) A calculation of the biomass potential in the ocean (Whitman et al., 1998)

(Above) Estimate of Archaea dominance in the prokaryotic biomass in the subseafoor biosphere based on IPL analysis (Lipp et al., 2008)
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OK, here, I would like to ask you a question. Does entire subseafloor environment consist of gminimally habitable environmenth?@Actually, many scientists believe the existence of prosperous microbial communities in geologically and hydrogeologically dynamic subseafloor environments. Recently, I have been surprised to find out that there was a scientist who had clearly foreseen it over thirty years ago.@In a very famous article in Science by Corliss et al. in 1979, reporting the first discovery of deep-sea hydrothermal activity, young John A. Baross who was a postdoctoral fellow in Oregon State University suggested the prosperous bacterial communities beneath the basaltic lava covering the diffusing hydrothermal flows. Later in 1993, Baross published a paper with Jody Deming stating the possible existence of active subseafloor microbial communities beneath the hydrothermal vents, so-called as esubvent biospheref. This paper later became a guide and the first clue to my research to prove the subvent bisophere and to write a IODP proposal drilling the Okinawa Trough hydrothermal system. In fact, John Baross was my supervisor when I was in the first year of Ph.D. in University of Washington. This may make it a romantic story between teacher and student on the subvent biosphere as his Japanese pupil is now challenging his ambitious hypothesis crossing over the countries and generations. I would be cordially happy if John Baross would be also pleased with the successful IODP expedition.

(Above) The worldfs first scientific paper regarding the discovery of deep-sea hydrothermal activity published in Science, 1979. There was an amazing foresight written in this article.
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@Majority of the subseafloor microorganisms are gminimally aliveh, for they are fed by a limited amount of organic compounds made by photosynthetic activities on the Earthfs outer layers. However, the subvent biosphere just beneath the hydrothermal vents and the subseafloor bisophere in the vicinity of the hydrothermal systems are energetically rich and fertile. The key could be found in the hydrothermal fluids. The hydrothermal fluids are heated in a few kilometers deep in high temperatures of crust. In the hydrothermal reaction zone, the hydrothermal fluids reacts with rocks and magma at 400Ž or even higher, which dissolve abundant reductive chemicals of the rocks and magma into the fluids. These chemicals are fruits of the Earthfs internal energy and are called as egeofuelsf. Or, in another word, this hydrothermal fluid flow is a flow of a griverh that supplies the Earthfs internal energy to the deep-sea world. As many estuary regions on land where rivers meet the ocean are fertile with glight-dependant ecosystemh, the active hydrothermal fields where hydrothermal fluids meet the deep-sea may be nurturing a rich gdark ecosystemh. Saying, ea river runs through it, ocean crustf.

(Above) A schematic model of gsubseafloor riversh
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Well, getting too scientific or bored? Let me just joke about it to break the ice! I will tell you how I chose this field for the research. If anyone asked me like a mom asking her child gKen, my honey, where would you like to drill if you want to do a research on hydrothermal fluid spurting sites?h Then, I would surely answer as a forty-year-old child gI want to do Kairei Field in Indian Ocean! I want it all or nothing!h For the serious reason why I chose that site, please refer to Extremobiosphere Research Programfs website (Click Here) . So, why did I write a proposal of the IODP drilling for the Okinawa Trough hydrothermal system, although I wanted to go to Kairei Field in Indian Ocean? Well, I was tricked and cheated! In a way, it was a national plot. Anyway, I should stop joking here. In 2001, scientifically and realistically considering the most promising drilling targets to directly probe the functionally active, metabolically diverse subvent biosphere in the next ten years, the systems had to be in the vicinity of the major countries that led IODP with desirable conditions. Among them, the Okinawa Trough deep-sea hydrothermal systems seemed to possess the highest possibility of offering us the chances.
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What is the most distinctive characteristic of Okinawa Trough deep-sea hydrothermal systems? It is that the hydrothermal fluids contain extremely high concentrations of carbon dioxide and methane. In the long history of DSDP/ODP/IODP program, the drilling of active hydrothermal systems was carried out only a few times, and most of those drilling expeditions were targeted to the ones in the Mid Ocean Ridges. Actually, this drilling expedition is the first exploration of deep-sea hydrothermal systems occurring in the backarc rifting, continental margin. The more important factor is that the Okinawa Trough and Ryukyu arc hydrothermal systems are strongly associated with thick terrigenous sediments entrained by large rivers of China, the Yellow River and the Yangtze River. The Okinawa Trough hydrothermal systems represent a quite novel type among the global deep-sea hydrothermal systems. The abundance of organics-rich sediments and the occurrence in the backarc rifting setting directly cause the extraordinary high concentrations of carbon dioxide and methane in the hydrothermal fluids. Moreover, these two characteristics are linked with generation of the horizontally quite long gsubseafloor hydrothermal fluid flowh in the Okinawa Trough. The Iheya North field would be the one potentially hosting the longest fluid path and the greatest size of fluid catchment area in the world.

(Above) The ocean floor of Okinawa Trough. Upper left is the Yangtze River. The accumulated sediments are visible.

(Above) Several possible hydrothermal fluid path models hypothesized for the Iheya North Field. The vertical black bars indicate the proposed drilling sites.
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I introduced my own idea of the Iheya North hydrothermal system to form a great river under the ocean floor. So, what kind of gsubseafloor riverh is the Iheya North hydrothermal system classified into? In fact, it is thought that there are four representative types of great rivers characterized by the predominant energy source for primary production of the associating ecosystem included in the fluid, each one different from one another by different motive forces and so on (http://www-gbs.eps.s.u-tokyo.ac.jp/~taiga/index.html"). Each river is named as hydrogen, sulfur, iron, or methane river. The one found in Iheya North Field and other hydrothermal fields in Okinawa Trough are gthe methane great riversh. The methane great rivers are equivalent to the terrestrial great rivers with fertile ecosystems along their flows. In addition, Iheya North Field has been estimated to have the largest fluid catchment area. This also makes it similar to the Amazon River. Not only the flow area is extremely large, but with numerous branching tributaries that flow out of the tropical jungles on their journey, the Amazon River is exactly like the Iheya North hydrothermal field itself!
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It is now predicted that the entire hydrothermal circulation path of the Iheya North field is approximately a few tens of kilometers in horizontal distance, and a few kilometers in vertical distance. At every stages of the subseafloor river, different types of microbial communities are developed, and their activities give alterations of chemical compositions in the fluids and environments. The ambitious drilling investigation that intended to elucidate the entire interactions among microorganisms-fluids-solids at representative stages, is the IODP 601 Proposal. This proposal was first submitted to IODP in September, 2001. Nine years later, in September 2010, some sites of the drilling proposal were carried out as IODP Leg#331 by using Chikyu. However, in IODP Leg#331 expedition, only the estuary regions of Iheya North hydrothermal system are planned to be drilled. Therefore, the primary scientific objective will be gthe direct proving of the existence of the subvent biosphereh. Another important objective written in the IODP Proposal 601 is to investigate its gtropical rain foresth regions of Iheya North hydrothermal system, which are the places where the methane is actually produced. Due to the limited time available, this will be examined in the expeditions after next year.
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The research on hydrothermal fluid chemistry and microbial communities in the Iheya North field has been continued since 1997, almost annually, and we are convinced that the microbial ecosystem associated with the hydrothermal activity is the most extensively characterized in the world. There are approximately seven huge hydrothermal mounds in Iheya North field, and each mound has considerably different fluid chemistry. This is because of the hydrothermal fluid being boiled, so-called phase-separation and -partition of gas-enriched and -depleted fluids, and the formation of complex hydrothermal fluid channels in the subseafloor. This process will eventually result in the different mixing ratio of gas-enriched and -depleted fluids, for they have different mobility. Thus, there will be a variety of mounds hosting different hydrothermal fluid chemistry; some have more gaseous compounds, and others with higher salinity and so forth. We have proved for the first time in the world that such variability in hydrothermal fluid chemistry greatly affects the microbial communities inhabiting in the mounds. It was based on the studies using the in situ colonization devices deployed in the hydrothermal fluids, the hydrothermal fluids themselves and the available pieces of the hydrothermal mound deposits. However, these were indirect evidences. In IODP 331st expedition, we are expecting to directly prove the predicted model of formation and distribution of microbial communities just beneath the hydrothermal discharging area as well as the existence of functionally active, metabolically diverse subvent bisophere.

(Above) NBC mound, the largest hydrothermal mound in Iheya North field

(Above) A model of formation and distribution of microbial communities just beneath the hydrothermal discharging area of the Iheya North field.
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In IODP Leg#331 expedition, we will first sample piston cores from the sediments in the hydrothermal mixing zones with the least hydrothermal input. When the hard metal deposit appears, we will take 100-200m core samples by industrially conventional drilling. We will also try a challenging drilling operation pinpointing the hydrothermal mound of about 30m tall. The hole we drill will function as the artificial hydrothermal vent. However, if this drilled hole is left without any processes, it will soon be buried as if nothing has happened, and we do not want it to be wasted that way. Therefore, we will build artificial hydrothermal fluid flows by inserting corrosion-resistant metal pipes into the holes, which will enable hydrothermal fluid to jet out from the specific depth of subseafloor hydrothermal channel. These artificial hydrothermal vents will give us an excellent chance to directly take samples and examine the hydrothermal fluids that flow under the seafloor, which are difficult to collect during the ordinary expeditions. The artificial hydrothermal vents dug by Chikyu will be immediately surveyed by R/V Natsushima and ROV HyperDolphin. This way, the freshly venting hydrothermal fluids can be collected. We are planning to monitor the artificial hydrothermal vents for the coming years. In fact, the hydrothermal activities are going through dynamic changes in a short span of time than we imagine. Actually, the hydrothermal activities are dramatically affected and changed by natual events such as earthquakes and volcanic eruptions. It is only us, the human beings, that are not aware of those changes. Very few investigations are conducted to know how the physical and chemical characteristics of the hydrothermal fluids are changed, what kinds of microorganisms will settle first and which will pioneer the new frontier after such catastrophic events. By making an artificial hydrothermal vents, we can conduct a well established research of these processes. We will set an in-situ culture container at the depth of the hydrothermal fluid source in the artificial hydrothermal vent (Kandata System) in order to obtain indigenous microbial components present in the subseafloor hydrothermal fluids. We have developed new equipment that can tolerate up to 300Ž and can also sample the fluids preserving the in situ pressure and conditions. With the help of these systems and equipments, we are looking forward to gaining new perspectives on the microbial communities just beneath the hydrothermal vents. No one has yet succeeded. Do look forward exciting discoveries during the IODP expedition! Write to you soon.

(Above) Making an artificial hydrothermal vent and deployment of Kandata tool using the ROV
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