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81.
A method has been developed for determination of15N isotope ratio in nitrate nitrogen, which is a major analytical step in tracer experiments for studies of nitrate metabolism
in the marine environment. The method is based on diazotization of nitrite with sulfanilic acid following reduction of nitrate
to nitrite by a cadmium-copper column. The diazonium compound is then subject to the azo coupling reaction with 2-naphthol,
and the azo dye formed is extracted by a solid phase extraction column. The dye eluted from the column is collected, and total
nitrogen and15N content of the dye are determined by mass spectrometry. Sulfanilic acid can also remove preexisting nitrite by heating the
sample under acidic conditions before passing through the cadmium-copper reduction column. The average recovery of nitrate
nitrogen was 86%. A procedure for reducing the background nitrogen that derives from the analytical operations has been developed;
background nitrogen was limited to about 0.25 μg-atomN. The variation in the background nitrogen levels reflects the range of error in15N determination of nitrate nitrogen by this method. Application of the present method to a15NO3
− isotope dilution experiment for determination of nitrification rate in sea water is demonstrated. 相似文献
82.
Hiroshi Kuroda Manabu Shimizu Yuuichi Hirota Daisuke Ambe Hideki Akiyama 《Journal of Oceanography》2008,64(1):81-91
In order to specify a vertical thermal structure related to surface current variation on the continental slope in Tosa Bay,
Japan, we analyzed monthly regular hydrographic measurements in the years 1991–2004. Subsurface temperature below 200 m on
the slope was found to vary synchronously with the vertical displacement of the main thermocline around 200 m. It is shown
that the vertical-averaged temperature below 200 m is significantly correlated with an along-isobath/southwestward surface
current velocity on the slope. This correlation indicates that when a strong (weak) southwestward surface current is observed,
temperature below 200 m decreases (increases) simultaneously, that is, isotherms below the 200 m are displaced upward (downward)
together with the main thermocline. Moreover, when the strong southwestward flow is detected, across-isobath isotherms around
200 m slope upward toward the offshore direction. Furthermore, it is suggested that as the Kuroshio axis moves offshore south
of the bay, the southwestward flow tends to be weakened by the combined effect of other Kuroshio parameters such as transport
and stream width as well as the Kuroshio axis position. As a result, it is inferred that the correlation between the surface
current and subsurface temperature can be interpreted in terms of the formation and decay of an anticlockwise circulation
interacting with a cold eddy. 相似文献
83.
The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism
Hideki Wada Takamaru Ando Masayuki Suzuki 《Contributions to Mineralogy and Petrology》1998,132(4):309-320
Carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the Hida
metamorphic terrain, central Japan, display typical metamorphic fluid-enhanced isotopic zonations. Isotopic profiles obtained
from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion-enhanced
isotopic exchange may control these profiles. Carbon and oxygen isotopic behaviour in grain boundaries is remarkably different.
Oxygen isotopic troughs (18O depleted rims) around the calcite-grain boundaries are widely observed in this contact aureole, demonstrating that diffusion
of oxygen in calcite grain boundary dominates over lattice diffusion in calcite. In contrast, no difference is observed in
carbon isotopic profiles obtained from grain cores and rims. There is thus no specific role of the grain boundary for diffusion
of carbonic species in the metamorphic fluid during transportation. Carbon chemical species such as CO2 and CO3 ions in metamorphic fluid migrate mainly through lattice diffusion. The carbon and oxygen isotope profiles may be modelled
by diffusion into a semi-infinite medium. Empirically lattice diffusion of oxygen isotopes is almost six times faster than
that of carbon isotopes, and oxygen grain-boundary diffusion is ten times faster than oxygen lattice diffusion. Oxygen isotopic
results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was
parallel to the aquifer. From the stability of wollastonite and the attainment of oxygen isotopic equilibrium, we suggest
that diffusion of oxygen occurred through an aqueous fluid phase. The timescale of formation of the oxygen isotopic profile
around the wollastonite vein is calculated to be about 0.76 × 106 years using the experimentally determined diffusion constant.
Received: 14 January 1997 / Accepted: 23 April 1998 相似文献
84.
Mjelde Rolf Aurvåg Roar Kodaira Shuichi Shimamura Hideki Gunnarsson Karl Nakanishi Ayako Shiobara Hajime 《Marine Geophysical Researches》2002,23(2):123-145
The horizontal components from twenty Ocean Bottom Seismometers deployed along three profiles near the Kolbeinsey Ridge, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. Two profiles were acquired parallel to the ridge, and the third profile extended eastwards across the continental Jan Mayen Basin. The modelling requires a thin (few 100 m) layer with very high V
p/V
s-ratio (3.5–9.5) at the sea-floor in the area lacking sedimentary cover. The obtained V
p/V
s-ratios for the remaining part of layer 2A, 2B, 3 and upper mantle, correspond to the following lithologies: pillow lavas, sheeted dykes, gabbro and peridotite, respectively. All crustal layers exhibit a decreasing trend in V
p/V
s-ratio away-from-the-axis, interpreted as decreasing porosity and/or crack density in that direction. A significant S-wave azimuthal anisotropy is observed within the thin uppermost layer of basalt near the ridge. The anisotropy is interpreted as being caused by fluid-filled microcracks aligned along the direction of present-day maximum compressive stress, and indicates crustal extension at the ridge itself and perpendicular-to-the-ridge compression 12 km off axis. Spreading along the Kolbeinsey Ridge has most likely been continuous since its initiation ca. 25 Ma: The data do not suggest the presence of an extinct spreading axis between the Kolbeinsey Ridge and the Aegir Ridge as has been proposed earlier. The V
p/V
s-ratios found in the Jan Mayen Basin are compatible with continental crust, overlain by a sedimentary section dominated by shale. 相似文献
85.
Mjelde Rolf Kasahara Junzo Shimamura Hideki Kamimura Aya Kanazawa Toshihiko Kodaira Shuichi Raum Thomas Shiobara Hajime 《Marine Geophysical Researches》2002,23(2):169-183
On the Vøring volcanic passive margin offshore mid-Norway, NE Atlantic, a lower crustal body with P-wave velocities in the range of 7.1–7.7 km/s has been mapped by twenty two-dimensional Ocean Bottom Seismograph (OBS) profiles. The main aim of the present paper is to evaluate to what extent the lower crust is consistent with magmatic intrusions or serpentinized peridotite. The relatively low V
p/V
s ratios of 1.75–1.78 modelled for the lower crust under the continental part of the Vøring Plateau are consistent with mafic intrusions mixed with blocks of stretched continental crust, but not with the presence of partially serpentinized peridotites. The lower crustal high-velocity body is restricted to the area of the Late Cretaceous/Early Tertiary rift that lead to continental break-up in Early Eocene. The same model can explain the observations in the northern Vøring Basin, but in the central and southern Vøring Basin the seismic velocities do not preclude a model involving serpentinized peridotite in addition to intrusions and continental remnants. On the west Iberia non-volcanic margin a similar layer is interpreted as serpentinized peridotite. The existence of Moho reflections, the observation of S-wave anisotropy but absence of P-wave anisotropy, uncertainties regarding supply of water to allow for significant serpentinization and very low stretching factors compared with the west Iberia Margin, are among factors that argue against the presence of serpentinized peridotite in the Vøring Basin. 相似文献
86.
We have studied nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter by using engine-cooling sea water of a ferry boat. On Dec. 1986 and Jan. 1987, differences of PO4–P and DIN across the front are recognized. Especially in the latter case, differences of nutrients concentrations across the front are very obvious. But differences of nutrients across the front on Feb. 1986, Feb. and Mar. 1987 are not obvious. Inspite of winter,Akashiwo had happened in Osaka Bay, nutrients mostly have already been utilized by phytoplankton in inner part of Osaka Bay. Consequently, differences of nutrients concentrations across the front are nearly zero. 相似文献
87.
88.
Silicate to Nitrate Ratio of the Upper Sub-Arctic Pacific and the Bering Sea Basin in Summer: Its Implication for Phytoplankton Dynamics 总被引:2,自引:0,他引:2
Isao Koike Hiroshi Ogawa Toshi Nagata Rumi Fukuda Hideki Fukuda 《Journal of Oceanography》2001,57(3):253-260
Consumption of silicate and nitrate (Si:N molar ratio) in the upper layer of the pelagic subarctic Pacific in summer was evaluated by a regression analysis of silicate vs. nitrate concentrations at the upper 100 m depth. Based on data of three cruises, the pelagic subarctic Pacific can be classified into two groups. First group is characterized by roughly 1:1 consumption of silicate and nitrate, and occupies rather larger area of subarcfic Pacific, i.e., the Gulf of Alaska and the Western Subarctic gyre (averaged slope of Si:N linear regression: 1.21, n = 10 and 1.45, n = 9, respectively). Second group is the regions of the Bering Sea basin and the Oyashio region, and showed higher silicate consumption compared to that of nitrate (averaged slope of Si:N linear regression: 2.14, n = 9 and 2.36, n = 3, respectively). The Si:N difference observed is possibly attributed to relative contribution of diatoms production among the phytoplankton assemblages in the regions, i.e., dominance of diatoms production in the regions of the second group. Higher accumulation of ammonium at the bottom of euphotic layer in the summer Bering Sea basin would also contribute to increase consumption ratio of Si:N amounts. 相似文献
89.
Hideki Nagashima 《Journal of Oceanography》1971,27(1):1-6
The reflection and breaking of internal waves on a sloping beach were studied in a small wavetank filled with water and petroleum. The dependence of the reflection coefficient of the internal waves on wave steepness and on beach slope is found to be very similar to that of surface waves. The reflection coefficient is small for the very gentle slope, increases rapidly as the slope increases, and becomes almost constant for the steep slope. The reflection coefficient decreases with increase of the wave steepness. Also, the transition slope at which the coefficient curve has the maximum gradient increases with increase of the wave steepness. Breaking pattern of the internal waves is classified into four types; breaking, semi-breaking, wrinkle-generating, and non-breaking. Their dependence on beach slope and wave steepness is examined. The regular sequence of the four breaking types from breaking to non-breaking is observed with decrease of wave steepness or with increase of beach slope. 相似文献
90.
Isamu Aida Tokutaro Hatori Morio Koyama Hideki Nagashima Kinjiro Kajiura 《Journal of Oceanography》1972,28(5):207-219
To investigate the response characteristics of a bay to tsunamis, field measurements of long-period waves have been carried out at Onagawa and Okachi Bays, both of which face the Pacific Ocean in northern Japan. In Onagawa Bay, the observed transfer function is in good agreement with the prediction based on the one-dimensional numerical model, in the period range larger than about 15 minutes. The response of shorter periods seems to be influenced by the two-dimensionality of the bay. The oscillations within Onagawa Harbor are also discussed with respect to the relative amplitude and phase at two stations inside the harbor and it is estimated that the reflection coefficient at the waterfront is about 0.7. In Okachi Bay, the oscillations in the period range larger than about 10 minutes could be explained by a Y-shaped model of the bay. The dominant oscillations offshore of these two-bays are found to be the mode with the motion predominantly in the direction normal to the shelf orientation, and the estimated power spectral density of incoming waves in deep water varies asf
–2,f being the frequency. The waves of lateral modes, such as edge waves on the shelf, are small and of minor importance to generate bay oscillations of longer periods. 相似文献