We review seismological studies on structure of the Earth's deep interior. First, we describe spherically symmetric Earth structure and discuss its geophysical implications. Second, we show three-dimensional mantle structure revealed by seismic tomography and discuss its geophysical implications. Then, we briefly review various anomalous and interesting features found in the lower mantle and the inner core.
The recent progress of the studies on high pressure and high temperature phase transformation of earth materials are reviewed. A brief introduction on the basis on the chemistry and mineralogy of materials composing crust and mantle is also included. Several new high pressure minerals including the post-perovskite phase of MgSiO3, post-stishovite phases of SiO2 such as CaCl2 type, a-PbO2 type phases, which are likely to exist at the core-mantle boundary has been reported. Magma is highly compressible and compatible with iron relative to coexisting minerals, indicating existence of a melt-crystal density crossover at high pressure. The dense melt may play important roles at the core-mantle boundary together with in the early magma ocean stage of the earth's evolution. We can expect existence of gravitationally stable melts in the ultra low velocity layer at the core-mantle boundary. The study of the lower mantle and core is one of the most important target in the material science of the earth.
Plate motions provide the most basic information on plate tectonics. I explain how to describe plate motions on the Earth mathematically, and how they can be determined. I review the history of the determination of global plate motions, the most recent of which has been derived by space geodetic techniques.
Recent progress of seismic studies on plate boundary structures gives us impressive features with sporadic seismic reflectors and splay-type large faults found near and on the subducting plate boundary, which show the complicated geomorphology derived from the faults and subducting oceanic island and ridge. Seismic activity within the slab together with overriding sedimentary and metamorphic rocks also strongly suggests fractures due to dehydration reactions. Further, the finding of incompatibility among strong seismic reflections and strong seismic activity and/or the asperity along the plate boundary leads us to imagine that the free fluid occupying many cracks might control differences between the asperity and the non-asperity of the plate boundary. In this paper, we briefly review this recent progress in seismic and material sciences from field research on plate boundary structure and dynamics.
Recent developments in studies on the generation of magmas in the upper mantle are reviewed in this paper. This review focuses on mid-ocean ridges, where melting processes are believed to be simpler than those in other tectonic environments, thereby facilitating extensive application of clear-cut models. There are, however, still fundamental unsettled issues in magma generation beneath mid-ocean ridges. They are : (1) depth of initial melting, (2) depth of final melting, (3) style of melt transportation, (4) initial source composition, and, (5) heterogeneity. An attempt is made to clarify these points on the basis of petrologic and geochemical studies on abyssal peridotites and mid-ocean ridge basalts (MORB). A change in the style of melt transport from near fractional (chemical isolation) to near batch (permeable flow) melting is necessary to reconcile the observed behavior of major and trace elements in abyssal peridotites, suggesting the importance of resolving the melting history for each peridotite that has kept its own identity throughout the melting processes.
Current trends in research on history of life are briefly reviewed. Since the 1990s study on deep past focusing on early life on Earth and Mars has become popular. This trend often called astrobiology will be a main stream in earth science in this century because it involves the latest human issues, such as global environment, energy, food, world population, and search for habitable planets outside the solar system, in addition to conventional studies on the evolution of Earth and life. Studies on chemofossils of nanometric scale and on geochemical proxies for evaluating paleoenvironments will be the most important targets in this research field. Inevitable in Japan are overhaul of the current domestic-oriented atmosphere in the geological community and deployment of a new research style under a long-term scope.
A new research field is introduced for strata science in geology. The new stratigraphy is that a layer, a bed and/or a band of “a year, a month, a day, and several hours” we actually experience everyday, are defined from strata. In this paper we introduce the following four case studies of high-resolution determination for 1) annual beds, 2) historical river-flooding beds, 3) tidal bands, and 4) cross-beds. We also describe new information obtained from the results of these high-resolution stratigraphic studies, which include : discovery of millennial oscillations of solar cycle from the 500 Ka lake varves (annual beds) date determination of every fluvial-flooding beds from the intercalated human wastes and, 600-million-year history of Earth's rotation detected from an annual band in fossils and tidal beds in strata.
Ocean Drilling Program (ODP) revealed that huge amount of bacteria exists in subsurface environment which extends probably up to 1.5 km beneath the seafloor, and a recent study suggests that this extends in continental subsurface as well. A study in shallow aquifer shows that bacteria exhibit high activity under the environmental constraint. Dynamic interaction between microorganisms and the Earth will be soon unveiled, which may enforce us to rewrite evolution of life and its interaction with the development of the Earth environment.
This paper describes past climate and environmental changes during the past 101 to 105 year time scale obtained by recent studies on ice cores from Arctic and Antarctica. Shallow ice cores from Greenland and Svalbard show clear North Atlantic Oscillation (NAO) signals and explosive volcanic activities in the Northern Hemisphere and the equatorial regions. A deep ice core drilled to 2503 m at Dome Fuji, Antarctica covers the past 320 ka, which includes 3 glacial-interglacial cycles with Milankovitch cycles of about 20, 40, and 100 ka. Major chemical compositions and microparticle flux show high concentrations in glacials and low concentrations in interglain high-middle latitudes during glacial-interglacial cycles. The Dome Fuji deep ice core contains 25 visible tephra layers. An analysis of the chemical compositions shows the possible source volcanoes in and around the Antarctica.
Research on factors of climate variations on a seasonal to multi-decadal timescale is surveyed. However, it is difficult to fully cover wide-ranging research on climate systems including the latest results. This paper focuses on phenomena such as QBO that interact with the other factors. Oceans, which have a close relationship with climate change, are considered. Although there is overlapping with dissertations in another chapter, the main contents are as follows 1) ENSO is a quasi-periodic air-sea interaction, which has been studied closely. If evolvement of ENSO is predicted, it will make seasonal weather forecasts more precise. 2) The effects of stratospheric QBO on climate systems in the troposphere might have been exercised as grave cool damage that occurs in summers when QBO was in the W-phase, and some correlations have been found. QBO probably holds a significant key explaining climate variations. Therefore, elucidation of the QBO mechanism that influences the troposphere can be expected. 3) The relationship between solar activities and climate remains obscure. However, some influences of solar activities on the tropospheric circulation have been felt through sea surface temperature or interaction with stratospheric QBO. 4) In the air-sea interaction the ocean responds to solar radiation more slowly than the atmosphere, so the ocean seems to play a dominant role in long-lived teleconnections such as PDO. In addition, regime shifts of oceans sometimes have major effects on climate. We cannot discuss climate change without referring to oceans. 5) Global warming is in progress. As a result, shifts in general circulation might lead to abnormal weather, which means increased danger of frequent developments of the Okhotsk high, which is responsible for cool summer damage. 6) It is important to evaluate which factors contribute greatly to climate change. Understanding the mechanisms of weather fluctuations ranging from a few months to several years is a pressing matter to prevent recurrence of meteorological disasters.
The oceans play important roles in the formation of the earth's climate, and in climatic variations and change. One of these important roles is meridional heat transport due to oceanic general circulation, especially three-dimensional thermohaline circulation through the entire water column. The oceans transport a huge amount of heat-as much as that of the atmosphere. Accordingly, the north-south gradient of surface air temperature is greatly mitigated. Corresponding to global warming due to increases of greenhouse gasses, the oceanic heat content hasincreased sharply. Global warming might cause a weakening of the strength of thermohaline circulation.
Urban heat island phenomena, which are known as high temperature occurrences in the central part of a city, would be estimated to become much greater in a large city as Tokyo. There have been many studies on urban heat island phenomena in the field of meteorology, climatology, architecture and city planning. Thus overall feature of urban heat island phenomena including their mechanisms became clear from observational and numerical studies. However, the detailed characteristics of urban heat islands such as the long term warming trends of urban temperatures and the seasonal/diurnal variations in local scale temperature distribution are not fully discussed. This paper aims at clarifying the spatial and temporal structure of urban heat island phenomena in Tokyo metropolitan area as a case study in connection with anthropogenic energy consumption and diurnal wind fields based on the high density meteorological observational system in Tokyo Metropolis.