Chemical monitoring of volcanic gas using remote FT-IR spectroscopy at several active volcanoes in Japan

Chemical compositions of volcanic gases of several Japanese active volcanoes have been monitored from distant safe places since the beginning of the 1990s using an FT-IR spectral radiometer. For absorption measurements, an infrared light source behind volcanic gas emissions is necessary in a volcanic environment. In the early observations, infrared radiation from hot lava domes (Unzen volcano) and hot ground heated by high-temperature fumaroles (Usu, Aso, and Satsuma-Iwojima volcanoes) were used as infrared light sources. However, these sources were not available in many cases. This remote FT-IR method became more commonly applied to chemical monitoring of volcanic gases emitted from the summit or slopes of active volcanoes using scattered solar infrared light as infrared light sources (Sakurajima, Miyakejima, and Asama volcanoes). To date, eight species have been measured using this method: SO₂, HCl, HF, CO, CO₂, COS, SiF₄, and H₂O. The observations indicate that volcanic gases for each volcano have different chemical composition on a SO₂–HCl–HF ternary diagram in spite of similar tectonic settings, suggesting that vapor/melt volume ratios during volcanic gas formation differ among volcanoes. During more than 15 years of monitoring, chemical changes in volcanic gases attributable to ascent of magma were observed only at Asama, where HCl/SO₂ and HF/HCl ratios in the eruptive period were higher than those in non-eruptive period because of scrubbing of more soluble components in surface hydrothermal systems in the non-eruptive stage or solubility-controlled fractionation processes. Results show that these parameters are the most prospective ones among the various parameters measured using the remote FT-IR method to monitor volcanic activities.     

Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses

An historical objective analysis of subsurface temperature and salinity was carried out on a monthly basis from 1945 to 2003 using the latest observational databases and a sea surface temperature analysis. In addition, steric sea level changes were mainly examined using outputs of the objective analyses. The objective analysis is a revised version of Ishii et al. and is available at 16 levels in the upper 700 m depth. Artificial errors in the previous analysis during the 1990s have been worked out in the present analysis. The steric sea level computed from the temperature analysis has been verified with tide gauge observations and TOPEX/Poseidon sea surface height data. A correction for crustal movement is applied for tide gauge data along the Japanese coast. The new analysis is suitable for the discussion of global warming. Validation against the tide gauge reveals that the amplitude of thermosteric sea level becomes larger and the agreement improves in comparison with the previous analysis. A substantial part of local sea level rise along the Japanese coast appears to be explained by the thermosteric effect. The thermal expansion averaged in all longitudes from 60°S to 60°N explains at most half of recent sea level rise detected by satellite observation during the last decade. Considerable uncertainties remain in steric sea level, particularly over the southern oceans. Temperature changes within MLD make no effective contribution to steric sea level changes along the Antarctic Circumpolar Current. According to statistics using only reliable profiles of the temperature and salinity analyses, salinity variations are intrinsically important to steric sea level changes in high latitudes and in the Atlantic Ocean. Although data sparseness is severe even in the latest decade, linear trends of global mean thermosteric and halosteric sea level for 1955 to 2003 are estimated to be 0.31 ± 0.07 mm/yr and 0.04 ± 0.01 mm/yr, respectively. These estimates are comparable to those of the former studies.     

The diet of mesopelagic fish from the Pacific coast of Hokkaido,Japan

The diet of at least 28 species of mesopelagic fish from the Pacific coast of Hokkaido was examined. The dominant family was the Gonostomatidae (42%) which was represented by five species. The most abundant species wasCyclothone atraria which together with the other species of this genus preyed predominantly on copepods. Euphausiids and copepods were dominant in the diet ofGonostoma gracile. The next most abundant family was the Myctophidae (32%) which was represented by seven species. The dominant species,Stenobrachius nannochir, preyed mainly on copepods. Copepods were also the dominant food item of the other myctophids except forLampanyctus jordani which fed mainly on euphausiids. The other important family was the Bathylagidae (21%).Leuroglossus schmidti was the dominant species and its diet was more diverse with ostracods, copepods, molluscs and larvaceans being the most important food items.Bathylagus ochotensis had a similar diet. Copepods were the most important food items for all but a few species and their occurrence in the fish stomachs was related to the known vertical distribution of both predators and prey. Ostracods and euphausiids were also important prey items, the latter especially in large fish species. Molluscs and larvaceans were restricted to the two species of the family Bathylagidae.     

Wind- and density-driven circulation in a bay on the Sanriku ria coast,Japan: study of Shizugawa Bay facing the Pacific Ocean

Flow fields in Shizugawa Bay on the Sanriku ria coast, which faces the Pacific Ocean, were investigated using hydrographic observations for the purpose of understanding oceanographic conditions and the process of water exchanges in the bay after the 2011 earthquake off the Pacific coast of Tohoku. In spring to summer, density-driven surface outflow is part of estuarine circulation and is induced by a pressure gradient force under larger longitudinal gradients in density along with lower salinity water in the innermost part of the bay, regardless of wind forcing. In winter to summer, another density-driven current with a thermal structure is induced by a pressure gradient force under the smaller longitudinal density gradients in calm wind conditions. Particularly in winter, Tsugaru Warm Current water can be transported in the surface layer inside the bay. Wind-driven bay-scale circulation with downwind and upwind currents in the surface and deeper layers, respectively, is induced by strong longitudinal wind forcing under the smaller longitudinal density gradients, irrespective of season. Particularly in fall to spring, this circulation can cause the intrusions of oceanic water associated with Oyashio water and Tsugaru Warm Current water in the deeper layer. These results suggest that wind- and density-driven currents can produce the active exchange of water from inside and outside the bay throughout the year.     

Effect of the formation of EDTA complexes on the diffusion of metal ions in water

The diffusion coefficients of aquo metal ions (M^z+) and their EDTA complexes (M-EDTA^(z−4)+) were compared to understand the effect of EDTA complexation on the diffusion of metal ions by the diffusion cell method for Co²⁺, Ga³⁺, Rb⁺, Sr²⁺, Ag⁺, Cd²⁺, Cs⁺, Th⁴⁺, , and trivalent lanthanides. Most studies about ionic diffusion in water have dealt with free ion (hydrated ion). In many cases, however, polyvalent ions are dissolved as complexed species in natural waters. Hence, we need to study the diffusion behavior of complexes in order to understand the diffusion phenomenon in natural aquifer and to measure speciation by diffusive gradient in thin films (DGT), which requires the diffusion coefficients of the species examined. For many ions, the diffusion coefficients of M-EDTA^(z−4)+ are smaller than those of hydrated ions, but the diffusion coefficients of M-EDTA^(z−4)+ are larger than those of hydrated ions for ions with high ionic potentials (Ga³⁺ and Th⁴⁺). As a result, the diffusion coefficients of EDTA complexes are similar among various metal ions. In other words, the diffusion of each ion loses its characteristics by the complexation with EDTA. Although the difference is subtle, it was also found that the diffusion coefficients of EDTA complexes increase as the ionic potential increases, which can be explained by the size of the EDTA complex of each metal ion.     

Evaluation of tsunami impacts on shallow marine sediments: An example from the tsunami caused by the 2003 Tokachi-oki earthquake, northern Japan

A combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments. The 2003 Tokachi-oki earthquake, M 8.0, that occurred on 25 September 2003 off southeastern Hokkaido, northern Japan, generated a locally destructive tsunami. Maximum run-up height of the tsunami waves reached 4 m above sea level. In order to estimate the tsunami impacts on shallow marine sediments, we compared pre- and post-tsunami marine sediments in water depths of 38–112 m in terms of grain size, sedimentary structure, and microfossil content. Decreases of fine fractions, especially finer than very fine sand, which led to coarsen the mean grain size, were detected in the inner shelf of the northern part of the study area. Foraminiferal assemblages also changed in the coarsened sediments. On the other hand, the other shelf sediments largely unchanged or slightly fined. We also simulated the tsunami wave velocity and direction, and grain size entrained by the modeled tsunami. The numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45–95 m at the northern part of the study area. This is comparable with the actual grain-size changes after the tsunami had passed. However, some storms and tidal currents might also be possible to stir the surface sediments after the pre-tsunami survey, so we could not conclude that the grain-size changes had been caused only by the tsunami. Nevertheless, a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea.     

Determination of the second critical end point in silicate-H2O systems using high-pressure and high-temperature X-ray radiography

To determine the second critical end point in silicate-H₂O systems, a new method for the direct observations of immiscible fluids has been developed using a synchrotron X-ray radiography technique. High-pressure and high-temperature experiments were carried out with a Kawai-type, double-stage, multi-anvil high-pressure apparatus (SPEED-1500) installed at BL04B1, SPring-8, Japan. The Sr-plagioclase (SrAl₂Si₂O₈)-H₂O system was used as an illustrative example. A new sample container composed of a metal (Pt) tube with a pair of lids, made of single crystal diamonds, was used under pressures between 3.0 and 4.3 GPa, and temperatures up to ∼1600°C. The sample in the container could be directly observed through the diamond lids with X-ray radiography. At around 980 to 1060°C and pressures between 3.0 and 4.0 GPa, light gray spherical bubbles moving upward through the dark gray matrix were observed. The light gray spheres that absorb less X-rays represent an aqueous fluid, whereas the dark gray matrix represents a silicate melt. These two immiscible phases (aqueous fluid and silicate melt) were observed up to 4.0 GPa. At 4.3 GPa, no bubbles were observed. These observations suggest that the second critical end point in the Sr-plagioclase-H₂O system occurs at around 4.2 ± 0.2 GPa and 1020 ± 50°C. Our new technique can be applied to the direct observations of various systems with two coexisting fluids under deep mantle conditions.     

The geochemistry of volatile species in melt inclusions and sulfide minerals from Izu-Oshima volcano, Japan

Olivine-hosted melt inclusions in the O95 pyroclastic layer of Izu-Oshima volcano, Japan are basaltic to basaltic-andesitic in composition. The negative correlation between SiO₂ and H₂O in melt inclusions and reverse compositional zoning observed in olivine and other mineral phenocrysts is inferred to arise from mixing between a highly evolved and a less evolved magma. The latter is characterized by the highest S (0.15 wt.%) and H₂O (3.4 wt.%) concentrations among those described in reports of previous studies. The S⁶⁺/S_total ratios in melt inclusions were 0.64?–?0.73, suggesting a relatively high oxidation state (NNO + 0.87 at 1150°C). The presence of pyrrhotites, which are found only in titanomagnetite microlites, suggests that sulfide saturation occurred during microlite growth under at a sulfur fugacity (log fS₂) value of around + 0.5 for T = 1060°C. The groundmass glass compositions are more evolved (andesitic composition) than any melt inclusions containing high amounts of Cl (0.13 wt.%) but negligible H₂O (0.20 wt.%) and S (< 70 ppm), suggesting that Cl was retained in the magma, in contrast to S and H₂O, which degassed strongly during magma effusion.     

The spatial and seasonal distributions of air-transport origins to the Antarctic based on 5-day backward trajectory analysis

Transport of moisture-bearing air to the Antarctic is one of the important factors that control the mass balance of the ice sheet. Here, we investigate the distribution of air-parcel transport using a backward trajectory analysis over the entire Antarctic ice sheet, based on whether the air parcel was located inside or outside of Antarctica at 5 days before arrival. At this time, we considered the air from outside Antarctica to be moisture rich. Oceanic air was found to dominate in West Antarctica throughout the year, whereas air from inland was more prominently distributed around East Antarctica, especially in summer. In East Antarctica, there was a significant seasonal variation: air from inland dominated in summer, while air of oceanic origin dominated in winter. The distribution of air parcels that came from oceanic/inland sources was similar to the accumulation map (based on satellite data), which indicates that oceanic air parcels could be a substitute for moisture transport to the Antarctic. To determine the future impacts of climate change (e.g., sea level rise), more precise predictions of the variations in the surface mass balance will be required. Our results contribute towards the improved understanding of the spatial distributions of accumulation and aerosols found in Antarctic snow and ice cores.