Sumisu volcano,Izu-Bonin arc,Japan: site of a silicic caldera-forming eruption from a small open-ocean island

Sumisu volcano was the site of an eruption during 30–60 ka that introduced ∼48–50 km³ of rhyolite tephra into the open-ocean environment at the front of the Izu-Bonin arc. The resulting caldera is 8 × 10 km in diameter, has steep inner walls 550–780 m high, and a floor averaging 900 m below sea level. In the course of five research cruises to the Sumisu area, a manned submersible, two ROVs, a Deep-Tow camera sled, and dredge samples were used to study the caldera and surrounding areas. These studies were augmented by newly acquired single-channel seismic profiles and multi-beam seafloor swath-mapping. Caldera-wall traverses show that pre-caldera eruptions built a complex of overlapping dacitic and basaltic edifices, that eventually grew above sea level to form an island about 200 m high. The caldera-forming eruption began on the island and probably produced a large eruption column. We interpret that prodigious rates of tephra fallback overwhelmed the Sumisu area, forming huge rafts of floating pumice, choking the nearby water column with hyperconcentrations of slowly settling tephra, and generating pyroclastic gravity currents of water-saturated pumice that traveled downslope along the sea floor. Thick, compositionally similar pumice deposits encountered in ODP Leg 126 cores 70 km to the south could have been deposited by these gravity currents. The caldera-rim, presently at ocean depths of 100–400 m, is mantled by an extensive layer of coarse dense lithic clasts, but syn-caldera pumice deposits are only thin and locally preserved. The paucity of syn-caldera pumice could be due to the combined effects of proximal non-deposition and later erosion by strong ocean currents. Post-caldera edifice instability resulted in the collapse of a 15° sector of the eastern caldera rim and the formation of bathymetrically conspicuous wavy slump structures that disturb much of the volcano’s surface.     

Effects of tributyltin at concentrations below ambient levels in seawater on Caprella danilevskii (Crustacea: Amphipoda: Caprellidae)

Hatched juveniles of Caprella danilevskii (Crustacea: Amphipoda) were exposed to one of two concentrations of tributyltin (TBT) (1.1 and 10.7 ng TBTL(-1)) for 49 d at 20 degrees C. These concentrations are near or below ambient levels in seawater. In both treatments and control, the survival rate was 100% at maturation, and >85% at the end of the experiments. Females reached maturation at 20 (median) to 21.5d at instar VII, and repeated spawning 4-5 times during the experiment. The total number of juveniles per female decreased significantly from 39.5 in the control to 24.5 and 17.5 in 1.1 ng L(-1) and 10.7 ng L(-1) treatments, respectively. An earlier study reported that as the TBT concentration in seawater increased from a 0-10 ng L(-1) regime to a 10-20 ng L(-1) regime, the number of stations where Caprella spp. could be collected decreased along the coast of the Seto Inland Sea, of Japan. Thus, the present study indicates the possibility that the extremely low concentration of TBT measured in Japanese waters after 2000 lead to a reduction in reproductive success of Caprella spp.     

Biomagnification profiles of polycyclic aromatic hydrocarbons, alkylphenols and polychlorinated biphenyls in Tokyo Bay elucidated by δC and δN isotope ratios as guides to trophic web structure

Biomagnification profiles of polycyclic aromatic hydrocarbons (PAHs), alkylphenols, and polychlorinated biphenyls (PCBs) from the innermost part of Tokyo Bay, Japan were analyzed using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios as guides to trophic web structure. δ¹⁵N analysis indicated that all species of mollusks tested were primary consumers, while decapods and fish were secondary consumers. Higher concentrations of PCBs occurred in decapods and fish than in mollusks. In contrast, concentrations of PAHs and alkylphenols were lower in decapods and fish than in mollusks. Unlike PCBs, whose concentrations largely increased with increasing δ¹⁵N (i.e. increasing trophic level), all PAHs and alkylphenols analyzed followed a reverse trend. Molecular weights of PAHs are lower than those of PCBs, therefore low membrane permeability caused by large molecular size is an unlikely factor in the “biodilution” of PAHs. Organisms at higher trophic levels may rapidly metabolize PAHs or they may assimilate less of them.     

Carbon-14 age and chemical evolution of Ca(HCO3)2-type groundwater of age less than 8,000 years in a confined sandy and muddy Pleistocene aquifer, Japan

The Pleistocene Kimitsu aquifer was selected for examination of the relationship between groundwater age and chemical evolution of Ca(HCO₃)₂-type groundwater. For the most part, the aquifer is confined and composed mainly of quartz and feldspar with a small amount of calcite. The groundwater ages calculated by ¹⁴C were adjusted by using a carbon mass-balance method and corrected for effects of ¹⁴C diffusion. Groundwater ages in the Kimitsu aquifer vary from modern (upgradient) to approximately 2,400 years at 4.4 km from the edge of the recharge area. The ¹⁴C age was verified by groundwater velocity calculated from the hydraulic gradient and hydraulic conductivity. The confined groundwater evolved to Ca(HCO₃)₂-type around 50 years after recharge and this has been maintained for more than 8,300 years due to low chemical reactivity, derived from equilibrium with calcite, kaolinite and Ca-montmorillonite. In addition, high pH prevents the dissolution of Fe and Mn. Consequently, the rate of increase in electrical conductivity ranges from 10 to 30 μS/cm per 1,000 years. On the other hand, leakage from the deep region, which is recognized from high Cl^– levels, causes remarkable increases in CH₄ and HCO₃ ^– concentrations, resulting in an apparent sulfidic zone at 500-m depth in most downgradient regions.     

Assessing the resilience of Delhi to climate-related disasters: a comprehensive approach

The study addresses disaster risks in Delhi through a resilience approach. It utilizes the Climate Disaster Resilience Index (CDRI) tool, which assesses disaster resilience from five dimensions: physical, social, economic, institutional, and natural. Each dimension comprises 5 parameters, and each parameter consists of 5 variables. The study is carried out in the nine revenue districts of Delhi and reveals that East Delhi is least resilient and New Delhi is most resilient. The CDRI analysis in East Delhi points out the urgent need to focus on key parameters such as housing and land use, population, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. On the other hand, New Delhi is the most resilient due to all five dimensions, where most significant parameters responsible for its high resilience are housing and land use, population, income, employment, intensity and frequency of natural hazards, ecosystem services, and land use in natural terms. In addition, the overall results of all nine districts show an inverse relationship between resilience score and population density. For example, districts with higher population density show low resilience and vice versa. Moreover, districts located on hazard-prone areas show low resilience. For example, East Delhi and North East Delhi scored low resilience because they both are situated on the Yamuna flood catchment areas. The study further develops key suggestions that are required to address disaster risk in all nine districts of Delhi and discusses future implications of CDRI to address city??s vulnerability. The approach??s distinctness is reflected through its consideration of micro-level diversities and presents some implications to resilience.     

Farmers’ adaptive practices for drought risk reduction in the northwest region of Bangladesh

Being an agrarian region, the northwest part of Bangladesh frequently experiences recurrent droughts over the last decade. To cope with this insidious disaster, the farmers in this region practice various adaptation measures through their own efforts with institutional support. But these efforts and support are not sufficient for farmers to survive droughts. In this light, this study assesses the adaptive capacity of farmers along with institutions to develop suitable drought adaptation policy in the context of this region. The drought adaptive practices developed in this study are mainly adopted from the unique approach called socioeconomic, institutional and physical. Results reveal that establishment of mango orchard, vegetable gardening and community health care service would be helpful in enhancing drought resilience at community level. Moreover, an important policy message from this study suggests that validation of these practices through government offices, research institutes and other relevant organizations can help to develop an appropriate drought adaptation policy for this region. Similarly, by performing these practices from national to local level, farmers as well as communities in this region will be able to effectively sustain their livelihoods against droughts.     

A long‐range and high‐resolution underwater acoustic positioning system

Abstract

It is desired to track the location of an underwater data collecting platform using acoustic range data. A long‐range and high‐resolution acoustic system for underwater locating has been investigated. The system provides continuous and highly accurate tracking of a platform referenced to bottom‐mounted buoys. Each reference buoy contains an acoustic transponder, which is used to obtain ranging data from the transponder to the platform. The transponder has a signal source that is phase‐modulated by a maximal‐length binary sequence and a correlation processing unit to be capable of detecting received acoustic signals with high SNR in a noisy environment or in attenuation due to long‐range propagation, and to identify multipath acoustic signals. The acoustic system has been designed and sea tests tried. The results of that experiment have yielded capability of a submeter underwater acoustic positioning system.