Organic geochemistry of the Japan Sea sediments-1: Bulk organic matter and hydrocarbon analyses of Core KH-79-3, C-3 from the Oki Ridge for paleoenvironment assessments

Organic geochemical study of bulk organic matter (OM), hopanoid hydrocarbon and normal hydrocarbon (C₂₃C₃₅) was conducted for a 936-cm-long sediment core sample from the Oki Ridge of the Japan Sea (Core KH-79-3, C-3; 37°03.5 N, 134°42.6E, water depth 935 m). Stable carbon isotopic ratios were also measured for both bulk OM and individual hydrocarbons. The following results were obtained: (1) The weight ratios of total organic carbon to total nitrogen range from 6.2 to 9.4 in the core. The ¹³C values of bulk OM range from –25.1–20.7%.. The ¹³C values of OM in the sections of 140190 cm are lower (–25–24) than those in the other sections (–23–21). This result indicates that OM in the core except for the 140190 cm sections is essentially of marine origin. (2) The ¹³C value of diploptene (a hopanoid hydrocarbon) in the last glacial maximum (LGM), is –66.3 (vs. PDB), which indicates it originating in methanotrophic bacteria. This result provides evidence to support for the previous ideas (Oba et al., 1980, 1984; Masuzawa and Kitano, 1984) that the bottom waters in the Japan Sea were anoxic in LGM. (3) Long chain (C₂₃C₃₅) n-alkanes of higher-plant wax origin were found throughout the core. Their concentration is high in 140190 cm in depth, suggesting that eolian dust load was high in LGM. (4) The n-alkane/TOC ratio increases with decreasing ¹³C values of bulk OM. This result indicates that the load of terrestrial (probably eolian dust-derived) OM to the Japan Sea became higher in colder climates. (5) The CPI values of long-chain n-alkanes are different in different ¹³O stages of paleoclimate, probably reflecting variations in species of terrestrial higher plants as a result of climatological adaptations.     

The inventory and chemical characterization of dissolved proteins in oceanic waters

One-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and high resolution two-dimensional electrophoresis (2-DE) were applied to separate protein molecules in dissolved organic matter (DOM) from oceanic waters. Results were: (1) The 2-DE distinguished a total of 412 protein spots in 10 samples from five water columns over the Pacific, although fewer than 30 proteins were resolved as bands from the identical samples by SDS-PAGE. (2) Major and ubiquitous protein bands (34 and 39 kDa proteins) on the SDS-PAGE gel were resolved into horizontally spread arrays (trains) of spots on the 2-DE gels, indicating that these bands were a mixture of protein species that have the same molecular weight (MW) but different isoelectric points (pIs). (3) Proteins that exhibited such electrophoretic patterns on the 2-DE gels were glycosylated with variable linkages between the sugar and polypeptide chains. (4) N-terminal amino-acid sequencing demonstrated that individual spots within each train of spots had identical N-terminal amino-acid sequences.The N-terminal amino-acid sequences of the 39 and 34 kDa glycoprotein spots in samples collected at different sites were also identical. Protein isoforms with the same amino-acid sequence but different glycosylation profiles, termed glycoforms, were often observed on the 2-DE gel. Thirty-one and 24 spots on the 2-DE gels were glycoforms of two glycoproteins with MWs of 39 and 34 kDa, respectively; they were one protein species. The glycoforms of the 39 kDa protein were identified as a low molecular weight alkaline phosphatase (L-AP) of Pseudomonas aeruginosa PAO1 by a homology search through five amino-acid sequence databases. The present and earlier work indicates that all identified source organisms of dissolved proteins belong to the Pseudomonas group. We propose the hypothesis that proteins associated with membrane vesicles liberated from a minor member of the bacterioplankton assemblage, the marine Pseudomonas group, are one of the important sources of dissolved proteins in oceanic waters. This hypothesis may apply to the source pathway and survival not only of proteins and also to the universally occurring bacterial peptidoglycan and lipopolysaccharide components in DOM.     

Mean circulation induced over bottom topography by mesoscale variabilities in the Kuroshio Extension

Circulation could be generated over bottom topography by vertical shrinking or stretching of a water parcel, in which potential vorticity is conserved. The water parcel moves up or down over the bottom topography yielding shrinking or stretching. In addition to a prevailing current which advects the water parcel in one direction, an oscillatory motion can also induce shrinking and stretching, and circulation is consequently generated over the bottom topography, once it is averaged in time. A two-layer quasi-geostrophic model has been used to reproduce mesoscale variabilities both in and under the Kuroshio Extension around the Shatsky Rise. A combination of TOPEX and ERS altimeters provided information on an eddy field near the sea surface, while a data assimilation method was used to reconstruct the flow field below the main thermocline. Among various mesoscale processes associated with the Kuroshio, it is remarkable that topographic Rossby waves trapped over the Shatsky Rise are generated by the upper-layer mesoscale variability. A persistent anticyclonic circulation is produced on the Shatsky Rise through a water parcel moving up and down over the bottom slope, and is consistent with the observed density anomaly in the WOA94.     

Radium isotopes in coastal and open ocean surface waters of the Western North Pacific

Using manganese-impregnated fiber extraction and high-efficiency gamma counting techniques, we measured the distribution of ²²⁸Ra and ²²⁶Ra in surface waters near the coast of Japan and in the western North Pacific. There is no evidence in our data that any significant amount of ²²⁸Ra is added to open ocean surface waters from the coastal waters around Tokyo Bay. High ²²⁸Ra concentrations (> 10 dpm/10³ kg), were observed along the Kuroshio Current as compared to < 2.5 dpm/10³ kg between 10° and 30°N of the central gyre, and hence the major source of ²²⁸Ra in the surface water is likely to be the East Asian continental shelf zones. A simple one-dimensional eddy diffusion and advection model is used to explain the observed decrease of ²²⁸Ra from coast to the open ocean. The model results indicate two mixing regimes across the Kuroshio Current System with apparent eddy diffusion coefficients of K_y = 4 × 10⁵ cm² s⁻¹ at distance y < 200 km from the coast, and K_y = 4 × 10⁷ cm² s⁻¹ at y > 200 km. Along 40°N where an eastward flow of the ‘Kuroshio Extension’ prevails, an advective flow of > 0.1 knot is consistent with the observation of nearly constant ²²⁸Ra along the track.The geographical distribution pattern of ²²⁸Ra is clearly different from that of atmospherically derived ²¹⁰Pb. Thus the ²²⁸Ra in surface water serves as a useful tracer that accompanies fluvially and coastally derived elements during their subsequent lateral transport toward the central gyre.     

Precipitation of authigenic uranium in suboxic continental margin sediments from the Okinawa Trough

Concentrations of U and Th isotopes in Okinawa Trough and East China Sea sediment cores were determined by isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) to investigate the behavior of redox sensitive uranium in suboxic hemipelagic sediments and determine their significance in oceanic uranium balance. ²³⁸U concentrations and ²³⁸U/²³²Th activity ratios in the East China Sea sediments showed no remarkable variation with depth. However, ²³⁸U and ²³⁸U/²³²Th ratios in the Okinawa Trough sediments were low in the surface oxidizing layer but increased where the suboxic condition was encountered. The distribution profiles of ²³⁰Th and ²³²Th concentrations were relatively constant with depth in both the Okinawa Trough and East China Sea sediment cores. These results suggested that there has been post-depositional precipitation of authigenic uranium within the suboxic Okinawa Trough sediment column. The post-depositional precipitation rates of authigenic uranium were estimated to be 47 ± 5 to >62 ± 8 ng cm⁻² yr⁻¹; these rates were comparable to those previously reported for several anoxic sediments. A mechanism controlling precipitation of uranium may be the downward diffusion of uranium U(VI), reduction to U(IV) and finally precipitation onto the solid phase. The accumulation rate of uranium for the Okinawa Trough sediments was approximately eight times higher than the world average rate reported for suboxic sediments. This removal of uranium in the oceanic budget increases the importance of the suboxic sediment sink.     

Large kinetic power in FRII radio jets

We investigate the total kinetic powers (L _j) and ages (t _age) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio of L _j to the Eddington luminosity (L _Edd) resides in 0.02<L _j/L _Edd<10. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E _c) exceed the energy derived from the minimum energy condition (E _min): 2<E _c/E _min<160. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron and positron) and/or protons.     

Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event

The stratigraphic architecture of sedimentary basin provides important constraints on the rheological structure of the upper mantle and the crust, eustatic events and tectonic movements. In this study, we examined the convective coupling between the uppermost mantle and ductile lower crust as a formation mechanism of sedimentary basins. In this mechanism, the lower crust is squeezed by the upper mantle flow associated with mantle diapiric upwelling, resulting in the surface subsidence and formation of sedimentary basin. We investigated the stratigraphic architecture by taking into account the horizontal migration of the upwelling in time and spatial domains. The sedimentary basin is characterized by both the thickness and formation period for its gross feature and the sequence stratigraphy. The decay of the upwelling causes the surface uplift, and some parts of sediments deposited during the surface subsidence are consequently eroded. The subsidence area moves as the activity of upwelling horizontally migrates, resulting in the formation of unconformity for the uplifted and eroded area over the previous upwelling. We also incorporated the effects of third order eustasy, with amplitude of 100 m and period of 1 Myr, into convective coupling model. An application of our model to Karatsu-Sasebo coalfield in the Tertiary of the northwest Kyushu, Japan, indicates that the stratigraphic architecture of sedimentary basin including two effects, i.e. convective coupling and eustasy, may provide important information about the viscosity structure of the lower crust and uppermost mantle and spatio-temporal growth and decay histories of the mantle diapiric upwelling.     

AFM study on surface nanotopography of matrix olivines in Allende carbonaceous chondrite

By means of nanoscale surface observation, we have proposed a new approach for investigating fine crystals of cosmic materials to reveal their origin and growth conditions. Several different morphologies of polyhedral fine olivines with faceted faces have been found in Allende carbonaceous chondrite (4.5 byr in geochronological age). In the present work, molecular level topography of the faceted matrix olivine by Atomic Force Microscopy (AFM) has successfully been performed. The matrix olivine found to have preserved growth step pattern on its surface even though quite long time has passed since they formed in the early Solar System. The surface pattern suggests that the faceted matrix olivine could have been condensed from the gas phase, and possibly that these olivine crystals had continued to grow under a rapid cooling condition (0.1-1 K s⁻¹). The estimated cooling rate agrees well with predictions based on hypothetical rapid heating and cooling events such as shock wave heating.