Bathymetric influences of the Emperor Seamounts upon the subarctic gyre of the North Pacific: Examining boundary current dynamics along the eastern side of the mountain ridge with an idealized numerical model

The possible influences of the Emperor Seamounts (ESs) upon the subarctic gyre of the North Pacific (NPSAG) were investigated by a series of numerical experiments. In the experiments, a two-layer ocean with a meridional mountain ridge was forced by seasonally varying wind stress. We focused on how the return ratio, the ratio of the boundary transport along the eastern side of the ridge to the interior Sverdrup transport, changes with ridge height, width and density stratification. It was found that the return ratio can be large if the ridge width is greater than the width of the viscous boundary layer. In this case, the bottom pressure torque determines the return ratio; the return ratio is almost proportional to the ridge height when the ridge height is small and some contours of planetary potential vorticity pass over the ridge. However, the return ratio is independent of the ridge height and decreases with the stratification when the ridge height is large and all the contours of planetary potential vorticity are closed. These dependences of the return ratio were understood in terms of barotropic and baroclinic components of the bottom pressure torque. Implications for the bathymetric influences of ESs on the actual NPSAG are also discussed.     

Interannual variability of North Pacific eastern subtropical mode water formation in the 1990s derived from a 4-dimensional variational ocean data assimilation experiment

The interannual variability of eastern subtropical mode water (ESTMW) formation in the North Pacific is examined using a new ocean dataset constructed by a 4-dimensional variational data assimilation experiment covering the decade of the 1990s. The volume of newly formed ESTMW varies due to interannual variability in the following three physical processes taking place in the surface layer: (1) convergence in the transport of surface saline water induced by Ekman flow in the vicinity of the formation region, (2) thermal stratification in the preconditioning phase in association with the insolation anomaly induced largely by low-level cloud coverage, and (3) wintertime surface cooling in the eastern subtropics. We find that, in addition to the surface forcing, the properties of both the ESTMW and the upper mixed-layer water are broadly controlled by the volume of the new ESTMW component, and that the variations in the upper mixed-layer water affect the properties of ESTMW formed in the following winter. Due to the combined effect of these processes, the ESTMW subducts down to subsurface layers with a wide range of σ_θ values lying between 24.8 and 25.4 and with significant interannual variation in water mass formation.     

Occurrence of triterpenyl acetates in soil and their potential as chemotaxonomical markers of Asteraceae

As a part of a wider study aimed at determining new molecular biomarkers in soils and sediments that could be specific for distinct vegetation types with respect to unravelling past changes in land use, we analysed the neutral lipid content of soil developed in the catchment of a small lake in central France. The ketone/acetate lipid fraction of soil under pasture or meadow contained a series of pentacyclic triterpenyl acetates with wide structural diversity, most being reported in soil for the first time. The restricted number of potential plant sources of triterpenyl acetates (some produced by a single species) underlines the potential of triterpenyl acetates as new biomarkers to track past vegetation change in palaeoenvironmental studies, when found in natural archives such as soil, sediments or peat.     

Simulation of atmospheric effect on the emergent radiation over a circular lake

The upwelling radiation at the top of the atmosphere is computed over a circular lake which is located in the uniform Lambert surface, using a modified version of the doubling-adding method. The radiance over the lake is discussed with respect to the atmospheric effect. The radius of the lake is assumed to be 0.5, 1, and 3 km. The observational site is located at altitude 30 km. The zenith of the observational site is located in the plane which is determined by the zenith of the center of the lake and incident solar direction. The zenith angle of the observational site to the center of the lake is fixed to 6.28°. The atmosphere is assumed to be homogeneous, which is composed of aerosol and molecule, where the model aerosol is of the oceanic or the water soluble types.Numerical simulation exhibits an extraordinary effect near the lake. The radiance of the lake against the surrounding depends upon the albedo of the surrounding surface. It increases with the increase of the size of the lake and decreases with the optical thickness. At large optical depth, the radiance depends upon the aerosol characteristics. It shows little dependence on the solar zenith angle if less than 60°.     

Double diffusive convection in a rotating system

Linear instability theory of double diffusive convection is generalized to a rotating system. For sufficiently large rotation, rotation has a stabilizing effect, and viscosity stabilizes most of oscillatory modes but destabilizes direct modes. The following behavior is found in oscillatory modes in the case of destabilizing temperature distribution and stabilizing solute distribution. With the fixed destabilizing temperature distribution (1) the system is stable when the stabilizing solute gradient is large, (2) it becomes unstable with respect to oscillatory modes when the gradient is less than a certain value. (3) When the gradient is reduced further, the system becomes stable again. This anomalous phenomenon happens only when the Prandtle number is less than unity and larger than the ratio of the diffusivity of solute and that of temperature, under the existence of rotation.     

A DETAILED CHEMICAL STUDY ON THE BARWISE CHONDRITE

Six fragments of the Barwise meteorite were analyzed for REE and eleven other elements (Al, Ca, Mg, Mn, Na, K, Cr, Fe, Co, Ni and Ba). In addition, two fragments were analyzed for Si and Mg. The chondrite-normalized REE patterns of six fragments studied show interesting systematic variations. Three fragments with relatively high La abundances show a negative Ce anomaly. Since the meteorite in question is a find, it could be suspected that the observed REE fractionations are due to terrestrial contamination. To examine this point, a soil sample from the find site was also analyzed for REE and major chemical elements. It is considered that several facts, especially, the relationships between La and SiO₂ and between SiO₂ and MgO, suggest the pre-terrestrial fractionation rather than the terrestrial contamination. Unexpectedly, it is shown that the REE fractionation observed in the investigated fragments correlates with the metal-silicate and the Fe-Co-Ni fractionations. In this connection, large metal grains were investigated for Fe, Co and Ni contents. A suggestion is presented that this chondrite was formed through the melting of the surface of a planetesimal and the subsequent collision, although the possibility of terrestrial contamination might not be ruled out.     

EXPERIMENTAL STUDIES ON BEHAVIORS OF MAJOR AND MINOR LITHOPHILE ELEMENTS IN VAPORIZATION UNDER EVACUATED CONDITION

In order to investigate the volatilities of major and minor lithophile elements, evaporation experiments by electron bombardment were carried out employing basaltic rock powder. The elements studied included Al, Fe, Ca, Mg, Mn, Na, K, Rb, Ba and REE. The source crucible was heated to about 2300 °K, and the vaporized material was collected at different distances from the source. The enrichment factors of studied elements in the material collected on the condensation plate were calculated relative to the starting material. Patterns of REE removed during flights between varying distances were also evaluated.     

An asteroseismic study of the β Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g -mode with frequency 0.3428 d⁻¹ reported before is detected in our spectroscopy. We identify the four main modes as  (ℓ₁, m ₁) = (1, 1), (ℓ₂, m ₂) = (0, 0), (ℓ₃, m ₃) = (1, 0)  and  (ℓ₄, m ₄) = (2, 1)  for   f ₁= 5.178 964 d⁻¹, f ₂= 5.334 224 d⁻¹, f ₃= 5.066 316 d⁻¹  and   f ₄= 5.490 133 d⁻¹  , respectively. Our seismic modelling shows that f ₂ is likely the radial first overtone and that the core overshooting parameter  α_ov  is lower than 0.4 local pressure scale heights.     

MOA-cam3: a wide-field mosaic CCD camera for a gravitational microlensing survey in New Zealand

We have developed a wide-field mosaic CCD camera, MOA-cam3, mounted at the prime focus of the Microlensing Observations in Astrophysics (MOA) 1.8-m telescope. The camera consists of ten E2V CCD4482 chips, each having 2k×4k pixels, and covers a 2.2 deg² field of view with a single exposure. The optical system is well optimized to realize uniform image quality over this wide field. The chips are constantly cooled by a cryocooler at ??80° C, at which temperature dark current noise is negligible for a typical 1–3 min exposure. The CCD output charge is converted to a 16-bit digital signal by the GenIII system (Astronomical Research Cameras Inc.) and readout is within 25 s. Readout noise of 2–3 ADU (rms) is also negligible. We prepared a wide-band red filter for an effective microlensing survey and also Bessell V, I filters for standard astronomical studies. Microlensing studies have entered into a new era, which requires more statistics, and more rapid alerts to catch exotic light curves. Our new system is a powerful tool to realize both these requirements.