Geochemistry of the acid Kawah Putih lake, Patuha Volcano, West Java, Indonesia

Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, S^tot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S₄O₆²⁻+S₅O₆²⁻+S₆O₆²⁻=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO₂/H₂S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant ³⁴S fractionation (ΔSO₄–S_e of 20‰), probably the result of SO₂ disproportionation in or below the lake. The lake waters show strong enrichments in ¹⁸O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.     

On the origin of subsecond pulses at 17 GHz

We have analyzed three flare events with subsecond structures in hard X-rays (CGRO/ BATSE) and 17 GHz data (Nobeyama radioheliograph). It was shown that microwave subsecond brightenings (SSB) were generated by directly precipitating electrons with energy of 100–200 keV from tiny regions close to footpoints. In two events, when high correlation between microwaves and X-rays was observed, the SSB can be interpreted in terms of gyrosynchrotron emission. Plasma emission seems to be a more credible explanation of the spontaneous pulses in the event when poor correlation with X-rays was observed.     

Relationship between the grid size and the coefficient of lateral eddy viscosity in the finite difference computation of the linear vorticity equation in the ocean

The finite difference analog of the linear vorticity equation for the mass transport in the ocean does not hold good unless the grid size is smaller than a certain number.I thank Profs. YaleMintz, AkioArakawa and TaroMatsuno for their valuable suggestions.     

Holocene lake development and glacial-isostatic uplift at Lake Skallen and Lake Oyako,Lützow-Holm Bay,East Antarctica: Based on biogeochemical facies and molecular signatures

The paleolimnology of two lakes which were isolated as a result of the crustal uplift during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica were studied. The focus was on temporal variations in the biogeochemical composition of sediment cores recovered from Lake Skallen at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine settings, as indicated by analyses of C and N contents, nitrogen isotopic compositions (δ¹⁵N), and major element concentrations. Changes in the dominant primary producers during the marine–lacustrine transition (marine diatom to cyanobacteria) at L. Skallen was clearly revealed by biogenic opal-A, diatom assemblages, and molecular signature from denaturing gradient gel electrophoresis (DGGE) with 16S ribosomal RNA (rRNA) gene analysis. Radiocarbon dating of acid-insoluble organic C suggested that the environmental transition from marine to fresh water occurred at 2940 ± 100 cal yr BP at L. Skallen and 1060 ± 90 cal yr BP at L. Oyako. Based on these data, a mean crustal uplift rate of 3.2 mm yr⁻¹ is inferred for the history of marine–lacustrine transition via brackish conditions. The geological setting causing glacio-isostatic uplift was the primary factor in controlling the transition event in sedimentary and biological facies.     

Aqueous sulfur speciation possibly linked to sublimnic volcanic gas-water interaction during a quiescent period at Yugama crater lake,Kusatsu–Shirane volcano,Central Japan

After the phreatic eruption in 1982–83, volcanic activities at Kusatsu–Shirane volcano had been decreasing and reached a minimum in 1990, had turned to a temporal rise in activity up to 1994 and then decreased again at least up to 1997. During this low-activity period we observed a relatively short (≤ 1 y) cyclic variation in polythionates (PT) in the Yugama lake water. Spectral power density analysis of the PT time-series by an autoregressive (maximum entropy spectral estimation, MESE) method indicates that the major frequency in the PT variations is 1.0 y^− 1 and the minor is 2–3 y^− 1 (1.0 and 0.3–0.5 y in periodicity, respectively). Annual variations in the lake temperature are ruled out for explaining these periodicities. We attribute these cyclic variations to a cyclic magnification-reduction in meteoric-water injection into a hydrothermal regime where volcanic gases from cooling magma bodies at depth and cooler oxidized groundwater come into contact with each other. This interaction may result in a periodical change in the composition and flux of SO₂ and H₂S gases being discharged into the lake and forming PT. From a phase deviation (2–3 months) in the cycles between the annual precipitation, including snowmelt, and the PT time-series, we estimated the maximal depth of a hydrothermal reservoir beneath the lake assuming a vertical hydraulic conductivity (5 × 10^− 3 cm/s) of the volcanic detritus around the summit hydrothermal system. Chloride in the lake water reached a maximum 1.5 years faster than PT. This is most likely due to a gradual elevation of the potentiometric front of a concentrated sublimnic solution in the hydrothermal reservoir. Variations of dissolved SO₂ and H₂S in the lake water were not consistent with those of the fumarolic gases on the north flank of the volcano. This fact together with additional observations strongly suggests that these fumaroles may have the same origin but are chemically modified by a subsurface aquifer. The PT monitoring at active crater lakes during a quiescent period can provide insight into the annual expansions and reductions of a volcano-hosted hydrothermal reservoir.     

Sapphirine-bearing orthopyroxene-kyanite/sillimanite granulites from South Harris, NW Scotland: evidence for Proterozoic UHT metamorphism in the Lewisian

Sapphirine-bearing orthopyroxene-kyanite (Opx-Ky) and -sillimanite (Opx-Sil) granulites have been found in the Lewisian complex of South Harris in northwest Scotland. In the Opx-Ky granulites, orthopyroxene and kyanite are intergrown in a stable mineral assemblage, which indicates metamorphic condition at 800–900 °C >12 kbar. Sillimanite inclusions within orthopyroxene suggest that sillimanite formed earlier; conditions are estimated at 950 ± 30 °C at 10 kbar from orthopyroxene isopleths for aluminous orthopyroxene (<9.7 wt%). In the Opx-Sil granulite, the orthopyroxene + sillimanite + garnet + sapphirine assemblage is stable at the peak metamorphic stages, indicating P-T condition of 930–950 °C, >8 kbar according to the FMAS petrogenetic grid, and similar conditions were obtained by using orthopyroxene-garnet geothermobarometers. The two types of orthopyroxene-aluminosilicate granulites indicate that the peak metamorphic conditions were over 900 °C, compatible with ultra-high temperature metamorphism. As accessory sapphirine occurs in several assemblages and with different compositions; it is interpreted to be formed at different stages of the metamorphism. These granulites were formed during Early Proterozoic high-grade metamorphism due to the emplacement of the South Harris Igneous Complex at c. 2170–1870 Ma, and are not related to the major metamorphic episode of the Badcallian/Inverian metamorphism at c. 2700–2500 Ma in the mainland Lewisian. Received: 17 July 1998 / Accepted 8 March 1999     

Characterization of sulfate ion in travertine

The mode of incorporation of sulfate ion in travertine was discussed on the basis of chemical compositions, i.r. and laser Raman spectra. These data strongly suggest that most of the sulfate ions in the calcitic travertine replace carbonate ions. This conclusion is in good harmony with the facts that calcite incorporates more sulfate ions than aragonite does and that the sulfate content of manganoan calcite decreases with increasing manganese content (Takano et al. 1977). Based on this conclusion, retarding effect of sulfate ion on the precipitation of calcite from solution was discussed.     

Coastal acoustic tomography system and its field application

The coastal acoustic tomography system (CATS), composed of five moored acoustic stations, has been constructed to measure current fields. The system is developed with special considerations in mind, including the use of Global Positioning System clock signals in the synchronization of the system clock timing among the multiple acoustic stations, and the use of the differently coded Gold sequences to identify the acoustic signals corresponding to individual stations from a received signal. The CATS was successfully applied to map the structure of strongly nonlinear tidal currents in the coastal sea. In spite of the limited spatial resolution caused by inadequate sound transmission data, the two-dimensional tidal vortices features of growth, translation, and decay processes are reconstructed through an inverse analysis of the acoustic travel time obtained among the station pairs. It is evident that the CATS is a powerful tool for measuring variable current fields generated in the coastal seas     

Surface currents around Hokkaido in the late fall of 1981 obtained from analysis of satellite images

This paper describes the characteristics of currents around Hokkaido using a current vector map compiled by chasing the displacement of sea marks on a pair of successive thermal infrared images taken from a satellite, NOAA-6. The points of some sea surface patterns showing distinctive features which can be commonly identified in both images are called Sea Marks≓. This sea mark chase method≓ has a great advantage over velocity measurements by boats or buoys, in that it gives a synoptic view of the velocity distribution over a broad sea area extending for some hundreds of miles on a short time scale of half a day.In order to investigate the current in the late fall of 1981, we used the data taken at 19:05 JST on 30 October and at 7:20 JST on 31 October. With these data taken with a 12 hr difference, the measurement accuracy of the speed of sea marks reached ±0.1 knot through geometrical correction. The velocity vectors of sea marks agreed with results of GEK measurements performed on those days, and also with the mean current pattern obtained in the past based on sea surface data.The most distinct features recognized were some cyclonic and anticyclonic eddies of the order of 100 km in diameter which dominated in the Kuril Basin of the Okhotsk Sea. They appeared clearly in the original NOAA images and their physical parameters were determined quantitatively from the vector map. These eddies were located in the region of decay of the Soya Warm Current and were rotating at a speed nearly as large as that of the current. The problems of what feeds energy to these eddies and how long they live remain to be solved in future studies.     

Study of a Bistatic Radar System Using VLBI Technologies for Detecting Space Debris and the Experimental Verification of its Validity

Space debris are increasing around the Earth. The observation of space debris is a key issue for the investigation and monitoring of space environment. But the observation opportunities and the detection ability are limited in existing monostatic radar systems. This paper proposes a bistatic radar which is composed of a transmitting station and a receiving-only station. A carrier wave modulated by PN-PSK signals is used in combination with a VLBI (Very Long Baseline Interferometry) recorder for range measurement between space debris and stations. The receiving radio wave is processed on the basis of VLBI techniques. Accordingly, the system is shown to have significant advantages over a monostatic radar. We actually formed a bistatic radar system, and observed a satellite in order to experimentally verify the validity. The configuration of the system, data analysis and the experimental results are described.