Origins of hydrocarbons in the Sagara oil field, central Japan

Abstract   We collected free-gas and in situ fluid samples up to a depth of 200.6 m from the Sagara oil field, central Japan (34°44'N, 138°15'E), during the Sagara Drilling Program (SDP) and measured the concentrations and stable carbon isotopic compositions of CH₄ and C₂H₆ in the samples. A combination of the CH₄/C₂H₆ ratios with the carbon isotope ratios of methane indicates that the hydrocarbon gases are predominantly of thermogenic origin at all depths. The isotope signature of hydrocarbon gases of δ¹³      < δ¹³     suggests that these gases in the Sagara oil field are not generated by polymerization, but by the decomposition of organic materials.     

Chemical Assessment of Oceanic and Terrestrial Sulfur in the Marine Boundary Layer over the Northern North Pacific during Summer

Dimethylsulfide (DMS) in surface seawater and the air, methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄ ²–) in aerosol, and radon-222 (Rn-222) were measured in the northern North Pacific, including the Bering Sea, during summer (13 July – 6 September 1997). The mean atmospheric DMS concentrations in the eastern region (21.0 ± 5.8 nmole/m³ (mean ± S.D.), n=30) and Bering Sea (19.9 ± 9.8 nmole/m³, n=10) were higher than that in the western region (11.1 ± 6.4 nmole/m³, n=31) (p<0.05), although these regions did not significantly differ in the mean DMS concentration in surface seawater. Mean sea-to-air DMS flux in the eastern region (21.0 ± 10.4 mole/m²/day, n=19) was larger than those in the western region (11.3 ± 16.9 mole /m²/day, n=22) and Bering Sea (11.2 ± 7.8 mole/m²/day, n=7) (p<0.05). This suggests that the longitudinal difference in atmospheric DMS was produced by that in DMS flux owing to wind speed, while the possible causes of the higher DMS concentrations in the Bering Sea include (1) later DMS oxidation rates, (2) lower heights of the marine boundary layer, and (3) more inactive convection. The mean MSA concentrations in the eastern region (1.18 ± 0.84 nmole/m³, n=35) and Bering Sea (1.17 ± 0.87 nmole/m³, n=13) were higher than that in the western region (0.49 ± 0.25 nmole/m³, n=28) (p < 0.05). Thus the distribution of MSA was similar to that of DMS, while the nss-SO₄ ²– concentrations were higher near the continent. This suggests that nss-SO₄ ²– concentrations were regionally influenced by anthropogenic sulfur input, because the distribution of nss-SO₄ ²– was similar to that of Rn-222 used as a tracer of continental air masses.     

Excess bottom222Rn profiles and their implications in the northwestern Pacific Ocean

Vertical profiles of excess bottom²²²Rn and potential temperature were measured at 23 stations in the northwestern Pacific Ocean. The Rn profiles were classified into the following three types: quasi-exponential (type E), benthic boundary layer (type B), and horizontally disturbed (type H). The ratio among types E, B and H was approximately 2 : 3 : 1.An apparent vertical eddy diffusivity (K) was calculated by applying a one-dimensional diffusion model to the Rn profiles of types E and B. Type E had K values ranging from 15 to 180 cm² s^?1 (average: 70 cm² s^?1). As to type B, K values for the benthic boundary layer (4.5–260 cm² s^?1, average: 120 cm² s^?1) were always more than an order of magnitude larger than those for the upper layer (0.2–35 cm² s^?1, average: 7 cm² s^?1), indicating more active vertical mixing in the benthic boundary layer than in the upper layer.Rn profiles were measured in regions where the bottom topography is known. It was verified that the occurrence of type H related closely with local bottom topographic features accompanied by lateral transient supply of Rn-rich or Rn-poor water.A couple of Rn profiles at the same location, measured at time intervals of several years, were compared with each other for three locations. The general characteristics of Rn profiles were shown to remain unaltered with time, while the fine structure of Rn profiles may have short-term variations caused by local bottom topography and fluctuations of bottom current as indicated in type H.     

Three‐dimensional microstructure of samples recovered from asteroid 25143 Itokawa: Comparison with LL5 and LL6 chondrite particles

In this study, the three‐dimensional (3‐D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring‐8 during the preliminary examination of Hayabusa samples. Moreover, the 3‐D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S‐type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3‐D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B.     

Recycling of manganese in the coastal sea,Funka Bay,Japan

The downward flux of Mn through the water column was directly measured using sediment traps. The Mn flux from the bottom sediment to the water column, and the removal rate of Mn in the bottom water were estimated from Mn gradients in the bottom water. The sediment traps were deployed more than ten times at the same station in Funka Bay, Japan. The trapped settling matter and filtered suspended matter samples were analyzed for Mn, Fe, Al and ignition loss. The observed downward flux of Mn through the water column in winter (1.3–2.8 μg/cm² /day) was generally an order of magnitude larger than that in summer (0.13–0.45 μg/cm² /day), and the Mn fluxes for both seasons were also greater than the accumulation rate of Mn in the bottom sediments (0.10 μg/cm ²/day). More Al was contained in the trapped settling matter than in the suspended matter, while Mn showed the opposite behavior. The Fe/Mn ratio of the residual fraction (obtained by subtracting the sediment component of the settling matter) was rather well correlated with the corresponding ratio in suspended matter. Settling particles are expected to scavenge suspended matter during their passage through the water column. The flux of Mn across the sediment—water interface was estimated from its vertical profiles in the water column to be 0.1–0.3 μg/cm² day. The residence time of Mn in bottom water was about one to several months. These results suggest that Mn is actively recycled between the water column and the sediments of the coastal sea.     

The kinematical mechanism for the perturbation of the rotational axis in the rotation of the elastic Earth

Kubo (Celest Mech Dyn Astron 110:143–168, 2011) investigated the kinematical structure of the perturbation in the rotation of the elastic Earth due to the deformation caused by the outer bodies. In that paper, while the mechanism for the perturbation of the figure axis was made clear, that for the rotational axis was not shown explicitly. In the present study, following the same method, the structure of the perturbation of the rotational axis is investigated. This perturbation consists of the direct perturbation and the convective perturbation. First the direct perturbation is shown to be (A − C)/A times as large as that of the figure axis, coinciding with the analytical expressions obtained in preceding studies by other authors. As for the convective perturbation, which appears only in the perturbation of the rotational axis but not in that of the figure axis, it is shown to be (A − C)/A times the angular separation between the original figure axis and the induced figure axis produced by the elastic deformation, A and C being the principal moments of inertia of the Earth. If the perturbing bodies are motionless, the conclusion of Kubo (Celest Mech Dyn Astron 105:261–274, 2009) holds strictly, i.e. the sum of the direct and the convective perturbations of the rotational axis coincides with the perturbation of the figure axis.