Since the discovery of rich microbial communities at and around seafloor hydrothermal sites, their extension towards the oceanic crust beneath the seafloor is of great interest not only for microbial physiology/ecology but also for a wide range of Earth and planetary sciences. How can the communities survive in such an extreme environment? What kinds of metabolism are in action? It is proposed that the sub-seafloor ecosystems are characterized by different kinds of chemosynthetic primary production (carbon fixation), all of which are supported by chemical energy supplied from the sub-seafloor aquifers. We designate the unseen aquifers as sub-seafloor TAIGAs (great rivers) which are responsible for a geochemical flux equivalent to or even larger than that of terrestrial river runoff (e.g. Wheat and Mottl, 2000). Besides, they are responsible for supplying nutrients to microbes beneath the seafloor. We hypothesize that there are four representative TAIGAs based on the chemical energy of compounds of sulfur, carbon (methane), iron, and hydrogen, all of which are supported by the TAIGAs. It is important to note that the sub-seafloor ecosystems are controlled extensively by or are mutually related to the types of TAIGA that flow at the site. The hypothesis can be tested through cooperative research among microbiologists, geochemists, geophysicists, and geologists.
Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as the distribution of microbial communities within the oceanic crust. From a global context, low-temperature hydrothermal systems located far from the ridge axes are of great importance, because of their large covered area. Our current understandings of seafloor hydrothermal systems come mainly from high-temperature systems on fast-spreading ridges, which are assumed to be typical. Recently, observations have been conducted on high-temperature systems at slow- and ultraslow-spreading ridges. In addition, low-temperature hydrothermal systems far from the ridge axis have been investigated. These findings enable us to obtain a new view of seafloor hydrothermal systems. This paper summarizes recent observational and modeling studies on low-temperature and high-temperature hydrothermal systems. First, we briefly plot seafloor hydrothermal systems and present some historical remarks. Then, we review the most important properties of the crustal structure such as the distribution of heat sources and permeability, which control hydrothermal circulation. These are described in terms of spreading rate. For instance, a hydrothermal system on a fast-spreading ridge is hosted by a quasi-steady magma chamber under the axis, and a system on an ultraslow-spreading ridges is hosted by long-lived tectonic faults at the axis. We also introduce recent numerical simulations both for low-temperature and high-temperature systems including the authors' studies. The main topic of current research is the pattern of circulation of both systems. High-temperature systems are controlled by the phase separation of seawater and the spatial heterogeneities of heat sources. Low-temperature systems instead are mainly affected by the local permeability structure instead. The presence of seamounts is thought to account for heat transport in the oceanic crust.
The recent Ocean Drilling Program (ODP) and submersible studies have verified the importance of fluid circulation below the seafloor and exchanges of water between the crust and the oceans. Heat flow data indicate the important contribution of low-temperature hydrothermal systems on ridge flanks, which transport more than 70% of global convection heat loss (= hydrothermal flux) from the seafloor. Global water mass flux of hydrothermal fluid on ridge flanks is estimated to be 4.8 × 1015 kg/year, which is much larger than the high-temperature hydrothermal fluid flux on the ridge axis. Chemical exchanges between oceanic crust and oceans through low-temperature hydrothermal processes on ridge flanks are important in the context of global geochemical budgets. The first opportunity to collect samples of formation fluid circulating within the oceanic crust was provided by the discovery of low-temperature hydrothermal fluid emanating from an outcrop located at the 3.5 Ma ridge flank of the Juan de Fuca Ridge. Drilling into basement oceanic crust and deploying Circulation Obviation Retrofit Kit (CORK) facilities on the drilled holes provided another opportunity for directly sampling formation fluid. Based on the database of the chemical composition of these fluids, coupled with the estimated global water mass flux through the ridge flank region, global geochemical fluxes can be calculated. An alternative estimation can be obtained by a mass balance calculation between the chemical composition of altered and unaltered oceanic crust samples obtained by ODP drillings. Both estimations demonstrate that uptake of Mg, K, Li, Rb, and C from seawater and addition of Ca, Si, Mn, and other metals to seawater contribute to globally significant geochemical fluxes. Hydrothermal processes at the ridge flank region enhance axial fluxes of some elements, but offset and cancel the axial fluxes of others, which is comparable to riverine inputs into the oceans for some chemical species. Hydrothermal fluid circulation at the ridge flank region represents a habitat that could potentially host a significant and unique subseafloor biosphere. Microbial activities in the deep sediment layer may be stimulated by the upward diffusion of formation fluid from the underlying basement. Several microbiological studies provide evidence for a unique microbial community within the subseafloor basement.
Deep-sea hydrothermal vents are among the habitats that host the most diverse microbial communities on the Earth. It is promised that hydrothermal vent microbial communities play a major role in the circulation of energy and materials in the global oceanic and suboceanic environments, and even provide important insights into the origin and early evolution of life on the Earth and extraterrestrial life on other planets and moons. Deep-sea hydrothermal vent ecosystems are strongly dependent on the primary production of symbiotic and free-living chemolithoautotrophic microorganisms that can obtain energy from inorganic substances such as H2S, CO2, H2, and CH4 derived from hydrothermal vent fluids. The diversity and abundance of these energy and carbon sources at hydrothermal vent fluids are, in turn, controlled by subseafloor physical and chemical processes such as fluid–rock interactions and phase-separation and -partition of fluids. Therefore, linkage between rock (magma), hydrothermal fluid, and ecosystem is a key to understanding how deep-sea hydrothermal ecosystems are generated and sustained. In this article, we approach this whole “Rock–Fluid–Ecosystem linkage” with the two separate sub-linkages of “Rock–Fluid linkage” and “Fluid–Ecosystem linkage”, which have not been addressed by the individual research fields of the Geochemistry of Hydrothermal Systems and Hydrothermal Vent Microbiology, respectively. Here, we overview the progress of understanding the “Rock–Fluid” and “Fluid–Ecosystem” linkages, both of which will establish the basis for an integrated “Rock–Fluid–Ecosystem linkage”.
High-pressure and high-temperature hydrothermal experiments were initially conducted to measure mineral solubility and growth rate. Since then, considerable efforts have been made to characterize the alteration assemblages produced by a wide variety of hydrothermal fluids in different rock types. Based on such information, the conditions of sub-sea floor hydrothermal systems and the formation processes of ore deposits were investigated. These studies significantly depended on many important experimental results obtained by a batch (closed)-type experimental system which gives equilibrium conditions. On the other hand, attention has been also paid to a flow-type experimental system, because natural systems can not only constrained by experiments under equilibrium conditions but, more importantly, by non-equilibrium experiments. Recently, hydrothermal experiments were carried out to better understand interactions among rocks, hydrothermal fluids, and microbes. It has been suggested that microbial ecosystems might be widely distributed within oceanic crusts and be sustained by chemical energy derived from water-rock interactions. However, little is known about the flux of energy and materials involved in microbial activity within the crustal aquifer because of technical difficulties in accessing sub-seafloor environments. A flow-type cultivation system simulating natural hydrothermal environments including crustal aquifers could provide insights into the ecological significance of microorganisms and their contribution to the biogeochemical cycle in global oceans and crusts.
Hydrothermal circulations supply a huge amount of chemical species into the deep sea. More than 99% of chemical species emitted from high-temperature hydrothermal fluids flow into the deep sea and construct deep-sea hydrothermal plumes. Observations of hydrothermal plumes have led studies of deep-sea hydrothermal vents, such as locating deep-sea hydrothermal vents, locating deep-sea volcanic eruptions, and calculating geochemical fluxes from sub-seafloor to deep ocean. Hydrothermal plumes affect the microbial community in deep seas by supplying many reduced chemicals, which are possible energy sources of chemolithotrophic microbes. This paper (1) reviews physical, chemical, biological studies of hydrothermal plumes and (2) discusses novel field survey technology and ecological infection of sub-seafloor to the deep-sea environment.
In deep-sea reducing environments, such as hydrothermal vent fields and cold seep areas, biological communities with huge biomass are often observed. Such communities associated with bacterial chemosynthesis, which are composed of species endemic to these environments, are founded with hydrothermal activities and succeed with changes of activities. Over a longer timescale, genetic deviations among local populations and speciation occur during the course of a series of activities and finally new faunal groups diverged. We attempt to estimate the ages of various hydrothermal phenomena on various timescales from 10 to 107 years on the basis of the evolutionary ecology of animals endemic to hydrothermal vents as part of the “Taiga project”. In this paper, we introduce communities in hydrothermal vent fields and describe the principals of methodologies for age estimation, which we are now planning, and the expected results.
As our understanding of seafloor hydrothermal systems grows, we recognize they are not always stable and sometimes show dramatic changes. In this review, the authors present a compilation of geochemical and geochronological studies that are helpful when investigating the evolving processes of submarine hydrothermal systems. Chapter II describes the systematics and methodology of three dating techniques with discussions on their application to minerals formed by seafloor hydrothermal activities. The K-Ar (Ar-Ar) technique is popular for dating igneous rocks, but it is not appropriate for dating hydrothermal minerals because potassium is a trace component of sulfide/sulfate minerals. Following recent progress, micro-analytical techniques applying laser fusion are applicable for dating fluid inclusions and/or hydrothermal alteration minerals, which could provide important geochronological information. Uranium and thorium series disequilibrium dating have been employed for previous geochronological studies of hydrothermal minerals obtained from submarine ore deposits. To cover a wide time range, it is necessary to use various combinations of parent and daughter nuclides. Applying ESR dating to hydrothermal minerals is a rather new challenge. Although it needs several investigations to establish the methodology, it could be a useful rapid dating technique for a time range of less than one thousand years. Chapter III introduces studies focusing on the evolution of seafloor hydrothermal activities over a short time scale (one week to a few years). Detection of event plumes associated with seafloor lava eruption brought an awareness of episodic hydrothermal activity triggered by magmatic perturbation. Subsequent dive studies revealed evolving geochemical processes, such as major changes of volatiles and elemental species concentrations of venting fluid. With remote real-time monitoring of acoustic T-waves generated by seafloor seismic activities, event detection and response cruises have been conducted successfully to investigate various evolving processes in more detail. Chapter IV introduces studies focusing on the evolution of seafloor hydrothermal activities over a long time scale (tens of thousands of years). Radiometric dating studies of hydrothermal minerals such as sulfide and manganese oxide collected from the TAG mound, which is one of the largest hydrothermal mound structures, reveal an age distribution over at least 15000 years separated by quiescent intervals lasting up to 2000 years. On slow spreading ridges such as the Mid-Atlantic ridge, major fracture systems focus the hydrothermal discharge at one place for more than one thousand years with repeated reactivation. In Chapter V, the authors discuss the direction of future studies. Although hydrothermal systems on mid-oceanic ridges have been well studied, those related to arc-backarc magmatic activities could provide more appropriate fields for studying the evolutionary process of submarine hydrothermal systems. Combining geochronological studies with geochemical and mineralogical studies would be important for reconstructing the evolution process in more detail.
Old Nakagawa River is located in eastern part of Tokyo, 6.68km long, and runs along Arakawa River. The river is semi-closed to Arakawa River. River water and sediment samples were collected from 18 and 5 sites from Old Nakagawa River and Arakawa River, respectively. River water samples were analyzed for Na+ and K+ by AAS (atomic absorption spectroscopy), anions (Cl-, SO42-, Br-, NO3-, PO43-) by ion chromatography, and trace metals (Cd, Cr, Cu, Mo, Ni, Pb, Zn) by ICP-MS (inductively coupled plasma mass spectrometry). River sediments samples were analyzed for mineral identification by XRD (X-ray diffraction), and for trace metals (Cd, Cr, Cu, Mo, Ni, Pb, Zn) by ICP-MS. Cr6+ concentrations in river water and sediment samples were analyzed by fixations of Cr6+ by CaHPO4. Five step extraction method by Hall et al. (1996) was used to clarify the proportion of trace metals in each step (extracted solution) for the river sediment samples. I-geo (geoaccumulation index) and EF (enrichment factor) for the trace metals calculated from analytical data on river sediments samples are very high, indicating that the river sediments are highly polluted. Cr6+ in the river water and sediments samples was not detected, although ΣCr in sediments sample is very high, indicating Cr is present as 3+ in the sediments and water, and Cr in sediments is not mobile. Trace metal elements are classified into three groups. They are (A) Cd and Zn which exist mainly as AEC (adsorption- ion exchangeable) and acid soluble (carbonate) fraction, (B) Cu and Pb which exist mainly as amorphous and Fe oxyhydroxide occluded fraction, and (C) Cr and Ni which exist as various fractions.
The global climate is known to have been relatively warm during the period from the 4th to 10th centuries, although there were slightly different fluctuation patterns locally and regionally. The present article addresses these differences, analyzing the results of previous studies. The warm period is known in Europe as the Medieval Warm Period. Evidence in Japan is also found from the 4th century to the 11th century. Because historical age divisions differ between Europe and Japan, the peak of the Warm Period from the 7th to the 10th century is classified as part of the ancient period in Japan. Therefore, the Warm Period in Japan has been proposed to be called the Nara-Heian Warm Period, Heian Warm Period or Little Climatic Optimum. Based on the water level changes of Lake Shinji in Shimane Prefecture, the present article discusses the warmer climatic conditions in the Heian Period. It also examines old agricultural settlements in the Tohoku District, northern Honshu. People came from Hokkaido or northern Honshu and cultivated rice in the northeastern-most part of Honshu in the 1st century B.C. It is thought that the effect of the warm current branch flowing along the Japan Sea Coast and emerging on the Pacific side through the Tsugaru Straight had an influence on the distribution of rice cultivation at this early stage. Finally, the article shows that the northward shift of the power front of the Central Government (Yamato Chotei) during the 7th to the 9th centuries occurred about 70-80 years earlier in Dewa, an ancient state on the Japan Sea side of Tohoku District, than in Mutsu, also an ancient state on the Pacific side. It is interesting to note, however, that the speed of the northward shift was almost the same on both sides, even though there were different political powers, situations and problems on either side. It is suggested that the northward shift was affected by the warming on the broader space scale.
Azumaya Volcano is a stratovolcano located slightly at the back arc side of the volcanic front in central Japan. Previous studies led to the publication of a geologic map and the K-Ar age of some lavas, but the stratigraphic relationships of the volcanic products and their eruptive history are still unclear. Some tephras that possibly erupted from Azumaya Volcano have been found in the North Kanto region. But, there are relatively few descriptions of pyroclastic products. This study presents the lithological and petrographical characteristics of products from Azumaya Volcano, especially the refractive indices of phenocrysts, because these data are very important for identifying products and reconstructing eruptive history. This study examined the adequacy of the identification of tephras of the previous studies and whether the source of these tephras is Azumaya Volcano from the distribution of tephra and comparing mineral composition and refractive indices of orthopyroxene, plagioclase, hornblende, and cummingtonite phenocrysts in proximal products and distal tephras. Because the refractive indices of the phenocrysts in the products distributed in Azumaya Volcano have unique characteristics, refractive indices are useful for identifying and correlating products. Distal tephras correlated in previous studies have similar characteristics, increasing the probability that the source of the SgP.2 tephra bed is the Azumaya Volcano. In addition, the volume of the SgP.2 tephra bed was calculated to be 0.85 km3 dense-rock equivalents (DRE) using its distribution.
We measured major inorganic ions and stable isotope ratios of nitrogen and oxygen of nitrate in the stream water in the Chichibu region during the course of nitrogen saturation. Nitrate concentration showed a high west-east gradient in the study area. Stable isotope ratios of oxygen in nitrate showed clear relationships with nitrate concentration. A direct relationship was apparent in the lower range of nitrate concentrations in that the stable isotope ratio of oxygen increases as the nitrate concentration increases. On the other hand, oxygen stable isotope ratios of nitrate hardly increase in the middle to higher concentrations of nitrate. This phenomenon may suggest that the oxygen stable isotope ratios of nitrate reflect a phase of the nitrogen saturation in the forest ecosystems.
A large pyroclastic eruption occurred around 7.3 ka from the Kikai caldera about 30 km north of Yakushima Island. Its pyroclastic flow and fall deposits covered the entire area of Yakushima Island and may have influenced the evolution of unique floras and faunas of Yakushima Island. Detailed field survey revealed that the Koya pyroclastic flow deposit spread from NW to SE, covering almost the entire area of Yakushima. A part of the southern coastal area remained from the pyroclastic flow due to local alignment of topographic ridges and valleys, which acted as barriers to the pyroclastic flows. Possible tsunami deposits associated with the Kikai-Akahoya eruption were discovered in the area below ca. 50 m above sea level along the northern coasts of Yakushima and Kuchinoerabujima Islands.
We analyzed the locations of pre-Angkorean (2-8th century) and early Angkorean (9th century) cities in Cambodia and Laos by interpreting aerial photographs and carrying out a field investigation. We studied Angkor Borei (southern Cambodia), Shresthapura near the Vat Phou temple (southern Laos), Sambor Prei Kuk (central Cambodia), Banteay Prei Nokor (southeastern Cambodia), Phnom Chissor (southern Cambodia) and Hariharalaya (in Roluos near Angkor in Cambodia). We produced geomorphological maps of each city, and analyzed geographical settings focusing on relationships between cities and water resources, locations of temples, residential, and paddy production areas. The results will be published in another paper, we have already submitted as an original article.
Investigations of disasters caused by past earthquakes are useful when taking measures against earthquake disasters that may occur in the near future. In western Saitama Prefecture, there have been few reports so far on damage caused by earthquakes occurring beneath the Tokyo metropolitan area; however, a remarkable description was found in the annual report of the Central Meteorological Observatory of Japan. According to the report, a slope in Hanno town failed over a width extending 640-660 m caused by the 1894 Meiji Tokyo earthquake. The author investigated the location of the failed slope and details of damage. A family in Kusumi, Hanno city (Hanno town at that time), suffered from a landslide caused by a past earthquake which is considered to be the 1894 Meiji Tokyo earthquake. The slope beside their residence extends for about 700 m to the east along the Hirayama ridge, and descends steeply toward the Iruma River. Many scars from small landslides are left on the entire surface of the slope. These topographical features suggest that several landslides occurred on this slope following the 1894 Meiji Tokyo earthquake. As a result, the author has come to the conclusion that the failed slope reported by the Central Meteorological Observatory of Japan was located along the Hirayama ridge, and several landslides occurred on this slope. It is possible to recognize that a strong quake shook Hanno town, which is located far from the epicenter.
To clarify regional differences and determinants of drainage network evolution on the Chinese Loess Plateau, a distribution map of drainage density is delineated from DEMs. In addition, the distribution map of drainage density is compared to other thematic maps. This comparison reveals that drainage density distribution corresponds to the distribution of landform types such as uplands or hilly lands. The relation between mean annual rainfall and vegetation cover ratio on each landform type is also clarified. On hilly lands, drainage density increases as mean annual rainfall increases from 300 mm to 500 mm. After mean annual rainfall exceeds 500 mm, drainage density starts to decrease if the vegetation cover ratio is more than 70%. The correspondence between drainage density and bedrock geology is not clear. Therefore, it is likely that landform types control the regional distribution of drainage density. In addition, if mean annual rainfall is more than 500 mm, drainage network evolution is limited by vegetation cover even on hilly lands.
Relative sea-level data of the Philippines can be used to reconstruct global sea-level histories because isostatic influences from the melting of gigantic ice fields formerly located on both North American and European continents during the last glacial age are not significant. Ages and elevations of tidal notches are mapped along the northern coast of the Luzon Island, Philippines, and the results indicate that sea level during the Holocene was punctuated by discrete sea-level high stands. The first high stand occurred between 7.5-6.0 ky BP when sea level reached of 1 m above the present mean low tide level (pmlt). This was followed at a second rise of sea level reaching from 1.8 m to 2.7 m above pmlt from 6.0 to 4.0 ky BP. A descending trend of sea-level was then observed and stayed at a level from 0.9 to 1.2 m above pmlt between 2.8 and 1.2 ky BP. Although the magnitudes of these Holocene high stands differ depending on the locations of Luzon Island due to tectonic histories, observed 3 Holocene high stands have been widely reported around the Philippines. Given that three sea level high stands during the Holocene have been found with similar timings in Japan, Vietnam, and Australia, they seems to represent global climate signals.
The purpose of this study is to investigate the energy policy of the City of Portland, Oregon, U.S.A., and obtain information on energy policy development that may be useful to local public entities in Japan. In response to global warming and future energy resource shortages, local public entities have begun to investigate energy policies. Portland has a reputation as a national leader amongst cities in the U.S.A. on energy policy. This study consists of document investigation, field survey, and interviews on the contents, methods, and achievements of the energy policy of the City of Portland. “City of Portland 1990 Energy Policy” achieved a 10% reduction of energy budget and energy consumption by the city over 10 years, as well as several other good results. It also gives helpful examples for our energy policy formulation: detailed feasibility planning, integration of energy policy into comprehensive city plan as a formal element, and focus on buildings and facilities in the city under a program called “City Energy Challenge” to show citizens the efforts being made by the city. Now, Portland is going to start new policy with the 2050 goal of an 80% carbon reduction.
Devastating earthquakes often cause serious disasters in Asia. In 1996, the Asian Seismological Commission (ASC) was established in order to reduce earthquake disasters in Asia through sharing our knowledge of seismology and experience on earthquakes, and by bridging science and technology, research and application, domestic efforts and international collaboration, and Asia-Pacific and the world. The 7th general assembly of ASC was held in Tsukuba in November 2008. It was the first ASC assembly to be held in Japan. We express our sincere appreciation to Tokyo Geographical Society for supporting this meeting.
Mitigating landslide hazards is the ultimate objective of the Japan Landslide Society and the general goal of this international conference. The conference was held at Sendai city, Japan. The major themes of counter measure, simulation and monitoring, environmental issues, risk evaluation, mapping, education and case studies were discussed through 40 oral presentations and 42 poster presentations. In particular, the Country Report Session presented clear strategies by exchanging and sharing technological knowledge, and obtaining a scientific understanding of landslide phenomena and hazards not only locally but also on a global scale. Representatives from Japan, China, Nepal, Pakistan, Vietnam, Thailand and Indonesia made presentations. The field trip was also very valuable because of the individual epochs and fine weather. More than 200 landslide specialists from 30 countries participated in the conference.
The quality of shallow groundwater and spring water was investigated in two study areas in central Japan and central Netherlands, which are considered to have many contrasting geographical features. Human activities and their backgrounds were also investigated to clarify genealogically the relationships between land-water quality and surrounding human activities. The study areas are located in the eastern part of Tokyo Metropolitan area in Japan (referred to as JP) and between the cities of Amsterdam and Utrecht in the Netherlands (NL). An additional small area (Js) within the JP area was also selected to supplement shallow groundwater quality in the area. For each study area, 105 water samples were selected from data collected, sources of which included field data, a web-accessible database and a published thesis. Major inorganic ion concentrations and latitude/longitude/altitude information were collected for the selected water samples. In each study area, 7 classes of 15 samples were based on total major inorganic ion concentrations, and the values of data collected were averaged within the classes. The class-averaged values of ion concentrations and of latitude/longitude/altitude are shown and trends observed in each area are described. Common factors and differences among study areas are: •The conditions controlling class distributions in both JP (incl. Js) and NL areas are considered to be the same in terms of regional structures. Differences in source and residence time of groundwater along with altitude largely control distributions, and horizontal differences in land use have small effects in addition. •General characteristics as well as ways ion-balances and latitude/longitude locations change along with classes differ among study areas. One cause is the existence of brackish groundwater in NL. The other is considered to be the difference in land-use allocation and associated water-use mixture in terms of their patterns. The above two causes of differences are linked, incorporating the fact that shallow groundwater from recent precipitation is present in areas where the land is drained and groundwater is disturbed by human activities. In conclusion, the formation of class distributions in both JP (incl. Js)and NL areas is strongly related to land-use allocation and associated water-use mixture. Differences in land use in terms of altitude are greater than those in terms of horizontal distribution, which led to the common regional structures controlling distributions.