Balloon-Borne Optical Counter for in Situ Aerosol Measurements

A new balloon-borne optical particle counter has been developed to make in situ measurements of stratospheric aerosols. The intensity of light scattered at 60° from the forward direction by individual particles is measured. Aerosol number concentrations in seven size channels can be inferred. The counter has been calibrated using polystyrene and polyvinyl toluene latex spheres. There is good agreement between measured and calculated individual pulse intensities for aerosol with radii from 0.16 to 2.6 µm. The size resolution is limited by broadening of the pulse count/pulse height spectrum, arising mainly from the photoelectron statistics of photomultipliers. Stratospheric aerosol measurements have been made using this instrument at Kiruna (68°N, 21°E), Sweden, in February 1995, and at Aire sur l'Adour (44°N, 0°W), France, in 1992, 1993, and 1994. The uncertainties in the measurements are discussed. The retrieved aerosol concentrations and size distributions are presented, and shown to be broadly consistent with measurements made by the University of Wyoming optical particle counter.     

Stable isotope-guided analysis of congener-specific PCB concentrations in a Japanese coastal food web

Organisms collected from a coastal ecosystem in Japan were analyzed for concentrations of 205 polychlorinated biphenyls (PCBs) congeners; analyses were guided by δ¹³C and δ¹⁵N measurements. The regression slopes of log PCB concentration on δ¹⁵N value are regarded as indices of biomagnification in food webs. The slope (wet weight basis) of ΣPCBs was +0.104; the slope (lipid weight basis) was close to zero. Lipid content increased from 0.06% in a primary producer to 8.32% in the highest trophic level consumer. Hence, biomagnification of ΣPCBs (wet weight basis) can be attributed to increase of lipid content through the food web. For most of the congeners, the slopes (wet weight basis) exceeded those (lipid weight basis) by ca. 0.10. Slopes increased with increasing PCB chlorination levels between chlorine numbers 1–6; slopes decreased at higher chlorination levels. This decrease is likely caused by a decrease in membrane permeability with increasing molecular weight.     

Seasonal variations in coastal debris on Awaji Island, Japan

The subject of our study was Awaji Island, an island located in the west of Japan that is surrounded by sea and that has serious problems relating to coastal debris. We conducted a long-term investigation focusing on three beaches and evaluated the results. The study was designed to develop an understanding of the actual situation, to inform local citizens, and raise their concerns about the problem of debris with a view to taking action against it. We obtained the following results: the amount, type, and ratio of debris changed according to weather and ocean conditions; debris also differs according to geographical conditions; social and economic activities of the surrounding area influence the type of debris encountered. Following this study, we have continued our investigation, and are continuing to gather data. At the same time, it is important to spread our ideas and enlighten people so as to encourage them not to dump debris. We hope that these actions manage to raise the level of consciousness among local citizens and to expand their anti-debris activities.     

Geology of the Kokchetav UHP-HP metamorphic belt, Northern Kazakhstan

Abstract Ultrahigh-pressure metamorphic (UHPM) rocks of the Kokchetav Massif of Kazakhstan contain metamorphic microdiamond and coesite inclusions inside rigid capsules such as garnet and zircon. Precambrian protoliths of the UHPM rocks were metamorphosed at around 530 Ma, at pressures of about 7 GPa, which suggests that crustal protoliths were subducted to depths of over 200 km. Primary UHPM minerals are poorly preserved due to partial obliteration by subsequent Barrovian overprint during exhumation and later collision events in Caledonian times. We report the results of detailed mapping of the Kokchetav Massif and use structural data to propose intrusion and exhumation mechanisms for the UHPM rocks. Detailed mapping revealed that many subvertical structures in the ultrahigh-pressure–high-pressure (UHP–HP) units were formed due to later folding. The primary structure appears to be subhorizontal and the total thickness of the UHP rocks is estimated at around 2 km. The first order structure is sandwich-like; that is, the UHP–HP units are separated from underlying low-P metamorphic rocks of the Daulet Series and from feebly metamorphosed to unmetamorphosed sedimentary strata on the top by subhorizontal faults. Kinematic indicators show top-to-the-south sense of shear along the top, and top-to-the-north displacement along the bottom boundaries. These shear senses, together with the observed metamorphic gradients, suggest that the thin UHPM sheet was extruded toward the north. We consider wedge extrusion to have been the most effective mechanism for the exhumation of the UHPM rocks.     

Current-sheet-associated radio sources and development of the magnetosphere of an active region revealed from 17 GHz and Yohkoh data

We study the evolution of the active region (AR) NOAA 7321 in which appeared a so-called `neutral-line-associated source' (NLS) on the basis of data of the Nobeyama Radioheliograph and Yohkoh/SXT. We provide a physical interpretation of the NLS in terms of a topological magnetic reconnection model in a quadrupole magnetic configuration and discuss its relation to the evolution of the active region. Two kinds of the NLS were observed at 17 GHz. One of them, `rising NLS', was found in the growth stage. The other was `stationary NLS' detected in the maximal stage of the AR. Their presence was associated with substantial expansion of the active region's magnetosphere and accompanied by gradual development of spine-like structures visible in soft X-rays before homologous long-duration arcade flares. We suggest that the rising 17 GHz NLS corresponded to a fragment of a `horizontal' current sheet moving upward. Bright X-ray spines were boundaries of that current sheet. Almost all bursts observed from 26 to 28 October 1992 which accompanied class C and M flares occurred in the rising NLS. Formation of magnetic X-point singularities is believed to be responsible for the low-lying NLS. Reversal of circular polarization due to the effect of radio wave propagation was detected in that NLS on the limb. The initial stage of the microwave burst of the long-duration X9 class flare on 2 November 1992 occurred in this NLS. We also revealed observational manifestations of the presence of `vertical' non-neutral current sheet in the spatial structure of this NLS before the flare.     

Physical properties of the shallow sediments in late Pleistocene formations,Ursa Basin,Gulf of Mexico,and their implications for generation and preservation of shallow overpressures

Understanding the evolution of abnormally high fluid pressures within sedimentary formations is critical for analysing hydrogeological processes and assessing drilling risks. We have constructed a two-dimensional basin model and have performed numerical simulations to increase the understanding of the history of fluid flow and shallow overpressures in the Pleistocene and Holocene formations in the Ursa basin, deepwater Gulf of Mexico. We measured physical properties of sediments, such as porosity and permeability, in the laboratory and estimated in situ pore pressures from preconsolidation pressures. We obtained porosity–effective stress relationships from measurements of bulk density, grain density and preconsolidation pressures in the laboratory. Porosity–effective stress relationships were also obtained from downhole density logs and measured pore pressures. The porosity–effective stress and porosity–permeability relationships obtained were applied in two-dimensional basin simulations. Results showed that high pore pressures developed shortly after sediment deposition. Peaks in pore pressure ratios were related to high sedimentation rates of mass transport deposits and the incision of the Ursa channel. Lateral flows from the area where the overburden is thick towards the area where it is thin have occurred at least since 30 ka. Present pore pressure and temperature distributions suggest that lateral flows play a role in re-distributing heat in the basin.     

Hybridization of a Shallow 'I-type' Granitoid Pluton and its Host Migmatite by Magma-Chamber Wall Collapse: the Tokuwa Pluton, Central Japan

The Miocene Tokuwa pluton of ‘I-type’ granitoidaffinity was emplaced discordantly into a Cretaceous to Paleogeneaccretionary complex and induced a contact aureole in whichvarious thermally metamorphosed rocks were developed, includinghornfels, metatexite, diatexite and cordierite-bearing tonalite(Crd-tonalite) of ‘S-type’ granite affinity. Thethermally metamorphosed rocks show low-pressure reaction texturesculminating in partial melting. Peak P–T conditions of3 kbar at 780°C are estimated on the basis of the TWQ thermobarometerfor the garnet-bearing rocks. The rocks in the contact aureoleexhibit a gradual transition from hornfels, through metatexiteand diatexite to Crd-tonalite. The Sr-isotopic composition atthe time of Tokuwa pluton emplacement at 12 Ma decreases systematicallyfrom metatexite (0·7100–0·7112) throughdiatexite (0·7078–0·7094) to Crd-tonalite(0·7067–0·7068); this trend is interpretedin terms of mixing between the Tokuwa magma and the aureolemigmatites. The field relationships, geochemical data, and isotopicdata collectively suggest that the emplacement of the Tokuwapluton triggered partial melting of the surrounding metasedimentaryrocks. Subsequent hybridization of the Tokuwa magma with themetatexite in variable proportions produced the Crd-tonaliteand diatexite. The hybridization was caused by invasion of theTokuwa magma into the migmatite zone, accompanied by gravitationalcollapse of the previously crystallized wall of the magma chamber.The data presented demonstrate that even a relatively low-temperature,shallow, ‘I-type’ granitoid pluton can induce contactanatexis and hybrid ‘S-type’ granitoid formationat the intrusive contact. KEY WORDS: contact metamorphism; hybridization; magma–host-rock interaction; migmatite; ‘S-type’ granitoid     

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.     

河南省舞阳县贾湖遗址出土的鲤科鱼类咽齿研究

本文对贾湖遗址出土的鲤科鱼类进行了研究,发现有11种可以确定到属或种的鲤科鱼类.现在生存在中国南方的鲤科鱼类在贾湖遗址的出土,证明当时这个地区的气候比现在要温暖.这些鲤科鱼类是当时居住在贾湖遗址的先民有选择性地进行捕捞的.该研究有助于推进考古遗址出土鱼类遗存的动物考古学研究.