Interior textures,chemical compositions,and noble gas signatures of Antarctic cosmic spherules: Possible sources of spherules with long exposure ages

Abstract– The interior texture and chemical and noble gas composition of 99 cosmic spherules collected from the meteorite ice field around the Yamato Mountains in Antarctica were investigated. Their textures were used to classify the spherules into six different types reflecting the degree of heating: 13 were cryptocrystalline, 40 were barred olivine, 3 were porphyritic A, 24 were porphyritic B, 9 were porphyritic C, and 10 were partially melted spherules. While a correlation exists between the type of spherule and its noble gas content, there is no significant correlation between its chemical composition and noble gas content. Fifteen of the spherules still had detectable amounts of extraterrestrial He, and the majority of them had ³He/⁴He ratios that were close to that of solar wind (SW). The Ne isotopic composition of 28 of the spherules clustered between implantation‐fractionated SW and air. Extraterrestrial Ar, confirmed to be present because it had a ⁴⁰Ar/³⁶Ar ratio lower than that of terrestrial atmosphere, was found in 35 of the spherules. An enigmatic spherule, labeled M240410, had an extremely high concentration of cosmogenic nuclides. Assuming 4π exposure to galactic and solar cosmic rays as a micrometeoroid and no exposure on the parent body, the cosmic‐ray exposure (CRE) age of 393 Myr could be computed using cosmogenic ²¹Ne. Under these model assumptions, the inferred age suggests that the particle might have been an Edgeworth‐Kuiper Belt object. Alternatively, if exposure near the surface of its parent body was dominant, the CRE age of 382 Myr can be estimated from the cosmogenic ³⁸Ar using the production rate of the 2π exposure geometry, and implies that the particle may have originated in the mature regolith of an asteroid.     

Fifteen years progress of the TRITON array in the Western Pacific and Eastern Indian Oceans

The Triangle Trans‐Ocean Buoy Network (TRITON) project by the Japan Agency for Marine-Earth Science and Technology began with deployment in the western tropical Pacific Ocean in 1998 and has shifted to steady, long-term observations since 1999. After on-site inter-comparison with the Autonomous Temperature Line Acquisition System mooring system of the Tropical Atmosphere and Ocean (TAO) array by the National Oceanic and Atmospheric Administration, the TRITON array became the international TAO/TRITON array in 2000 as a key component of the Global Ocean and Climate Observing Systems. The TAO/TRITON array took over from the TAO array, which was developed during the Tropical Ocean and Global Atmosphere program (1985–1994), and replaced the western part of TAO with new additional real-time measurements of salinity and ocean currents. In 2001, two TRITON moorings were deployed in the eastern Indian Ocean for capturing the eastern pole of the Indian Ocean Dipole. From this initiative, the Indian Ocean Observing System (IndOOS) was designed, and the Indian Ocean mooring array (Research Moored Array for Africa–Asian–Australian Monsoon Analysis and Prediction) was developed as a key component of IndOOS. In this paper, 15 years of progress in the TRITON project in the western Pacific and eastern Indian Oceans is reviewed with regards to scientific outcomes, technological development, and collaborations with international and domestic partners. Future directions for sustainable observation in the Pacific and Indian Oceans are also discussed.     

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.     

Geodesy in Japan

T. Inoh was the first who completed a nation-wide map of Japan, in the beginning of the 19th century. He determined geodetic positions by distance and angle measurements and by astronomical observations. When Japan entered into its modern era, about 100 years ago, the Military Land Survey was established and has conducted geodetic work in Japan ever since until the end of World War II. A German surveying system belonging to Helmert's school was adopted. The Ministry of Education organized later the Geodetic Commission which promoted the geodetic activities in cooperation with the Military Land Survey. Comparison between the first and second nation-wide triangulation results obtained by the Geographical Survey Institute (GSI), the successor of the Military Land Survey, brought out marked horizontal land-deformations associated with a large earthquake. Repetitions of levelling survey also make it clear that vertical land-movements, well consistent with tide-gauge observation data, take place in association with earthquakes. The extensive subsidence in the Northeast Japan may be explained by assuming a sinking lithosphere, as is argued by the theory of plate tectonics. On the other hand, most local movements are closely correlated to pre-, co- and post-seismic land-deformations. The nation-wide gravity survey carried out by the GSI disclosed a complicated gravity distribution in Japan. Ship-borne gravimeters have now been extensively working at sea. One of the recent highlights of gravimetric work is the detection of secular gravity changes which are in accordance with the secular changes of levelling data. A portable absolute-gravity measuring instrument was constructed by the Earthquake Research Institute although it is still in a testing stage. Much advance has been made in the astrogeodetic observation devices since 1950's.     

New pop-up type Ocean Bottom Seismometer

We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes in off-shore areas. With a 57 cm O.D. sphere of high tension aluminium alloy, the OBS system, including one vertical and one horizontal geophone, can safely operate on ocean floors of up to 6000 m depth for seismic observations. The amplified seismic data and the time code are directly recorded on the four-channel cassette deck for periods of up to one month. The frequency response curve throughout the recording and play-back system is flat for the range, 1–15 Hz (–3 dB). The anchor release and the geophone clamp are operated by an acoustic command signal.So far, we have deployed our OBS's 42 times in the ocean. All of the OBS's deployed have been recovered safely. Seismic data has provided seismological evidence for a number of processes associated with tectonism along subduction zones and spreading ridges (e.g., Eguchi et al., 1986).     

Generation of Small Meanders of the Kuroshio South of Kyushu in a High-Resolution Ocean General Circulation Model

The generation of small meanders of the Kuroshio south of Kyushu has been investigated using a high-resolution ocean general circulation model of the North Pacific Ocean. The small cyclonic meander develops in the region east of the Tokara Strait with a period of about one month, then propagates downstream along the Kuroshio path to the longitude of the Kii Peninsula, which is similar to the so-called trigger meanders for the formation of the large-meander of the Kuroshio south of Japan. It turns out that the generation of the small meander is a local phenomenon, strongly associated with anticyclonic eddies that propagate northeastward along the Kuroshio path in the East China Sea. The vorticity balance indicates that the accumulation of positive vorticity during the developing phase of the small meander occurs mainly from the balance between the stretching and the advection terms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some properties of surf-beats

Long ocean waves with periods of several minutes (surf-beats) were observed at a marine observation tower. We have analysed time series data of an envelope of incident swell, long period current velocity and surface elevation fluctuations. Current velocity was measued by an electromagnetic flow meter. Surf-beats amplitudeH ^(l) is shown to be proportional to 3/2 power of incident swell amplitudeH ^(s), and decreases with increase of depthh in proportional toh ^–1/2 such thatH ^(l) H ^(s) (H ^(s)/h)^1/2. Frequency energy density functionP _LL (f) of surface elevation had two dominant peaks whose frequencies were highly stable through the entire observational period. Cross-spectral analysis suggested that those peaks correspond to traveling edge waves caused by the excess momentum and mass flux in the surf zone. The forced long ocean waves predicted byLonguet-Higgins andStewart (1964) was ditected. Phase-shift and wave height of the wave with respect to those of incident swell envelope are shown to be in remarkable agreement with the predictions. However the forced long wave is only a minor component in the total energy of surf-beats. Current fields are shown to be largely composed of non-surface modes.     

Thorium concentration and the activity ratios230Th/232Th and228Th/232Th in sea water in the western North Pacific

The concentration of thorium isotopes and the activity ratios of²³⁰Th/²³²Th and²²⁸Th/²³²Th in sea water collected in the Kuroshio region, the mixing area of Oyashio and Kuroshio, the Japan Sea and the East China Sea in the western North Pacific were determined. Thorium isotopes were analyzed by α-ray spectrometry after separating them with an anion exchange resin. The average content of thorium (²³²Th) of 2.2×10⁻⁹ g/l was obtained in the open Pacific waters. The ratio of²³⁰Th/²³²Th is in accord with that of the top layer of the sediment in the same area. The high values of²²⁸Th/²³²Th ratio up to 36 were observed in sea water. The excess²²⁸Th in sea water may be due to the migration of²²⁸Ra through the water-sediment interface. Thorium content in suspended matter was 10 to 20% of the total thorium content in the Pacific water.     

A numerical simulation of the distribution of water temperature and salinity in the Seto Inland Sea

Constant flows, as well as oscillatory tidal flow, play an important role in the long-term dispersion of water in the Seto Inland Sea. Two kinds of numerical model (1-line and 2-line models) of the Seto Inland Sea have been developed to determine the role of density-induced currents, one type of the constant flow, in water dispersion in the Inland Sea. The seasonal variations of temperature, salinity and density fields are simulated and the density-induced current field is predicted at the same time. It is found that the most appropriate value of the longitudinal eddy diffusion coefficient,K _x, is 5×10⁶–7×10⁶ cm²sec^–1. The value of the overall mean dispersion coefficient is of the order of 10⁷cm²sec^–1 (Hayami and Unoki, 1970). Consequently, it is suggested that 50–70% of the total dispersion in the Seto Inland Sea can be attributed to currents other than density-induced currents,i.e., tidal currents, tide-induced currents and wind-driven currents.In winter, both density and velocity fields, calculated using the 1-line model, satisfy the conditions for the existence of a coastal front in Kii Channel and in the eastern Iyo-nada.