Clay Minerals in an Active Hydrothermal Field at Iheya‐North‐Knoll,Okinawa Trough

Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.     

Stable isotopes in precipitation in the volcanic island of Cheju,Korea

Stable isotopes in precipitation sampled at different locations and altitudes over the volcanic island of Cheju, Korea, were analysed to elucidate the circulation patterns of water over the island where groundwater is a major water resource and the characteristics of stable isotopes in precipitation inputs to the hydrological cycle are a very important indicator of groundwater flow. Areal and altitudinal variation of stable isotopes in precipitation showed the contribution of different air masses to the precipitation on mountain slope areas and in the atmosphere above and below the boundary at around 1000 m a.s.l. Seasonal change of the isotopic composition of precipitation also gave a good illustration of the influence of the dominant regional air currents on precipitation inputs. Copyright © 1999 John Wiley & Sons, Ltd.     

Estimation of heat flux through the eastern Bering Strait

We estimated the northward heat flux through the eastern channel of the Bering Strait during the ice-free seasons between 1999 and 2008. This is likely about half of the total heat flux through the strait. The net volume transport and heat flux through the eastern channel of the strait were estimated from multiple linear regression models with in-situ/satellite remotely sensed datasets and NCEP reanalysis 10 m wind. The net volume transport was well explained by the west-east slope of sea level anomaly and NNW wind component at the strait. On the heat flux, the contributions of both barotropic and baroclinic components were taken into account. Estimated volume transport and vertical profile of temperature were used to calculate northward heat flux through the eastern channel of the strait. The magnitude of the estimated heat flux is comparable to estimates from in-situ measurements. Averaged heat flux in the eastern Bering Strait between 2004 and 2007 was about 1.9 times larger than that between 2000 and 2003. Maximum heat flux occurred in 2004, and same magnitude of heat flux was estimated from 2005 to 2007. This resulted not only from the increase in northward volume transport but also anomalous warm water intrusion from the Bering Sea. Our results suggest a candidate among the important parameters controlling heat budget, which contributes to the Arctic sea ice reduction, whereas more studies are required to confirm that this mechanism is actually responsible for the interannual and longer timescale variability.     

Nondestructive Sensor Using Microwaves From Laser Plasma by Subnanosecond Laser Pulses

Conventional ground-penetrating radar (GPR) requires large-aperture antennas or long-span measurements to survey a remote location precisely. We propose a laser-driven GPR (LGPR) as a new detection method. LGPR uses microwaves from laser-produced plasmas as remote transmitters and can survey a remote location using a compact instrument. We performed numerical simulations to investigate the radiation mechanism of microwaves from laser plasmas and confirmed the pulsewidth of the laser suitable for LGPR. Experiments with subnanosecond pulse lasers clarified the feasibility and detection performance of LGPR.     

Identification of Pathways for Hydrogen Gas Migration in Fault Zones with a Discontinuous,Heterogeneous Permeability Structure and the Relationship to Particle Size Distribution of Fault Materials

Previous studies have reported that high concentrations of H₂ gas are released from active fault zones. Experimental studies suggest that the H₂ gas is derived from the reaction of water with free radicals formed when silicate minerals are fractured at hypocenter depths during fault activities. However, the pathways for migration of deep-seated fluids to surface are still unknown. In this study we performed quick, multipoint H₂ gas measurements across a fault zone using a portable gas monitor and a hand drill. The fault zone studied includes a smectite-rich fault core dividing two clearly distinguishable damage zones: granite cataclasite and welded tuff fault breccia. The measurements show that H₂ gas emissions collected in 2–3 h sampling periods from start of measurement range from 320.3 to 446.2 ppm/min in the granite cataclasite and 60.5 to 137.8 ppm/min in the welded tuff fault breccias. Negligible quantities of H₂ gas could be collected from the fault core. Particle size distribution analyses of fault rocks indicate that the granite cataclasite tends to be rich in particles that are finer, i.e., less cohesive and easy to disaggregate, which leads to the inference that the granite cataclasite has high permeability. Based on the H₂ gas measurements and the particle size distribution analyses, the H₂ gas is considered to have migrated in permeable damage zones mostly by advection with groundwater. Multipoint H₂ gas measurement will be effective in qualitative delineation of variations in permeability of regional structures.     

Evaluation of plastic energy dissipation capacity of steel beams suffering ductile fracture under various loading histories

The energy dissipation capacity of a structure is a very important index that indicates the structural performance in energy‐based seismic design. This index depends greatly on the structural components that form the whole system. Owing to the wide use of the strong‐column weak‐beam strength hierarchy where steel beams dissipate the majority of earthquake input energy to the structures, it is necessary to evaluate the energy dissipation capacity of the beams. Under cyclic loadings such as seismic effects, the damage of the beams accumulates. Therefore, loading history is known to be the most pivotal factor influencing the deformation capacity and energy dissipation capacity of the beams. Seismic loadings with significantly different characteristics are applied to structural beams during different types of earthquakes and there is no unique appropriate loading protocol that can represent all types of seismic loadings. This paper focuses on the effects of various loading histories on the deformation capacity and energy dissipation capacity of the beams. Cyclic loading tests of steel beams were performed. In addition, some experimental results from published tests were also collected to form a database. This database was used to evaluate the energy dissipation capacity of steel beams suffering from ductile fracture under various loading histories. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of Continuous 222Rn Monitor with Dual Loop System in a Small Lake

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time‐shifting correction in the dual‐loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.     

Correction: Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

In the Bandung basin, Indonesia, excessive groundwater pumping caused by rapid increases in industrialization and population growth has caused subsurface environmental problems, such as excessive groundwater drawdown and land subsidence. In this study, multiple hydrogeochemical techniques and numerical modeling have been applied to evaluate the recharge processes and groundwater age (rejuvenation). Although all the groundwater in the Bandung basin is recharged at the same elevation at the periphery of the basin, the water type and residence time of the shallow and deep groundwater could be clearly differentiated. However, there was significant groundwater drawdown in all the depression areas and there is evidence of groundwater mixing between the shallow and deep groundwater. The groundwater mixing was traced from the high dichlorodifluoromethane (CFC-12) concentrations in some deep groundwater samples and by estimating the rejuvenation ratio (R) in some representative observation wells. The magnitude of CFC-12 concentration, as an indicator of young groundwater, showed a good correlation with R, determined using ¹⁴C activity in samples taken between 2008 and 2012. These correlations were confirmed with the estimation of vertical downward flux from shallower to deeper aquifers using numerical modeling. Furthermore, the change in vertical flux is affected by the change in groundwater pumping. Since the 1970s, the vertical flux increased significantly and reached approximately 15% of the total pumping amount during the 2000s, as it compensated the groundwater pumping. This study clearly revealed the processes of groundwater impact caused by excessive groundwater pumping using a combination of hydrogeochemical methods and modeling.

     

The importance of local mean time in remote sensing for mapping megatidal zones

The local mean time is rarely debated in applied remote sensing, although it is a key parameter, especially for the geological mapping of coastal areas with high tidal ranges. French test sites are used to illustrate the role of this parameter. Depending from location and for an average time of acquisition of 11:00 UTC, the exposed tidal flat ranges from 55% (Baie des Veys), 80% (Mont Saint-Michel) to 100% (Cap-Ferret). Eight multisource satellite images were used in the Mont Saint-Michel Bay to draw the limit of the sea and evaluate the corresponding tidal flat's surfaces for various times of acquisition. The relation emphasizes some geometrical properties of the lower part of the intertidal zone. A NW–SE profile allows one to identify a distal part with a slope of 0.2% and a proximal part with a slope of only 0.06%. JERS 1-OPS and ALOS-AVNIR-2 data have been also compared to evaluate the progression of the halophytic vegetation, covering more than 6 km² between 1992 and 2007. From a methodological point of view, the ALOS-AVNIR-2 acquired on October 2007 is the first satellite data covering the Mont Saint-Michel Bay with a water elevation of only 2.56 m, i.e. a tidal flat free of water over 80% of its surface.     

Measurement of evapotranspiration in a winter wheat field

Daily evapotranspiration from a winter wheat field on the North China Plain measured by large‐scale weighing lysimeter was linearly related to that measured by the Bowen ratio energy balance (BREB) technique. Soil evaporation averaged about 23·6% of evapotranspiration from the post‐winter dormancy revival stage to the grain ripening stage in 1999. On clear days during winter dormancy, about half of the net radiation flux R_n was used to warm soil. During the revival stage, conductive heat flux G also used most of the incoming R_n, but the ratio of latent heat flux λE to R_n increased. During the stem‐extension stage, λE was about 50% of R_n; thereafter, λE/R_n increased continually, but G remained less than 10% of R_n. During the ripening stage, λE was almost 90% of R_n. Evaporative fraction (EF) can be expressed as a function of plant status and atmospheric boundary layer conditions. The relationship between EF and available energy under moderate air temperature and vapour pressure deficit conditions was examined for five combinations of aerodynamic and canopy conductance. Although the theoretical relationship indicates that EF should be highly correlated to soil water content, the correlation has been difficult to identify under field conditions. However, we observed that there exists a threshold value of R_n ? G, above which EF is less than 1·0, and that the threshold value is lower under soil‐water deficit conditions than under abundant soil‐water conditions. Copyright © 2002 John Wiley & Sons, Ltd.