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71.
Michinobu Kuwae Azumi Yamashita Yuichi Hayami Atsushi Kaneda Takashige Sugimoto Yoshio Inouchi Atsuko Amano Hidetaka Takeoka 《Journal of Oceanography》2006,62(5):657-666
In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation
(PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core
samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux—the best index of fall primary productivity in the BC—indicated a multidecadal-scale duration with a low flux (1943–1982)
and those with a high flux (1913–1943 and 1982–2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982
was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the
biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a
general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux
records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale
variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich
water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC,
and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC
primary productivity and the PDO. 相似文献
72.
Atsushi Kubokawa 《Journal of Oceanography》1995,51(2):207-224
Gyre-scale frontal structures, e.g., the Subtropical Front, have been well documented in the oceans. Although the generation mechanism of such a front remains unclear, it may be ascribed to the steepening of nonlinear planetary waves as discussed by Dewar (1992). To discuss the stationary wave characteristics and their shock formation in a two-layer wind-driven gyre, the present paper introduces a new coordinate, referred to as theSverdrup coordinate here, in which the Sverdrup function is used instead of the longitudinal coordinate, and especially, investigates the possibility of the frontgenesis caused by the Rossby waves emanating from the western boundary region. On theSverdrup coordinate, since the advection by the Sverdrup flow is in the direction normal to that of the Rossby wave propagation, the system becomes much simpler than that on the (x,y)-coordinate, and the solution to this coordinate does not explicitly depend on the distribution of the Ekman pumping, i.e., we can treat cases, in which the Ekman pumping is a function of bothx andy, in a similar way to the case with zonally uniform Ekman pumping. 相似文献
73.
During a cruise aboard the R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998 the particle number concentrations
and the major ionic components of size fractionated aerosols were measured to investigate the aerosol produced by marine biological
activity. Continuous low concentrations of nitrate (<1.8 nmol m−3), similar to the marine air background level, were found over the northwestern North Pacific (40–45°N) and the Sea of Okhotsk
(44–45°N). Over the Sea of Okhotsk, a high concentration of chlorophyll-a (5.4 mg m−3) in seawater was observed, and atmospheric concentrations of non sea-salt (nss-) sulfate (44 nmol m−3), methane sulfonic acid (MSA) (1.8 nmol m−3) and particle number in the size range of 0.1 < D < 0.5 μm (199 cm−3) were found to be 9, 7, and 2 times, respectively, higher than those in the background marine air. The increase in particle
number concentrations mainly in the size range of 0.2 < D < 0.3 μm was likely caused by the increase of biogenic sulfate over the high productive region of the Sea of Okhotsk. In
humid air conditions (R.H. > 96%), the increased biogenic sulfate that condensed the large amount of water vapor would not
have sufficient solute mass to activate as cloud condensation nuclei (CNN) and would remain as aerosol particles in the marine
air with frequent sea-fogs over the high productive region. Biogenic sulfate originating from dimethyl sulfide (DMS) would
gradually grow into the CCN size and continuously supply a great number of CCN to the marine air in the northwestern North
Pacific.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
74.
Rolando S. Balotro Atsuhiko Isobe Manabu Shimizu Atsushi Kaneda Takatoshi Takeuchi Hidetaka Takeoka 《Journal of Oceanography》2002,58(6):759-773
An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate
the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the
entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting
from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening
of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each
season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of
horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant
function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM).
The results revealed a small difference in the average residence times of materials within each season but a large seasonal
variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar
trend of variation between the seasonal values of average residence times.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
75.
Vertical profiles of210Pb and230Th in the deep water were analyzed by using a simple one-dimensional model. Both nuclides are considered to settle down with the velocity of 1×10–4 cm/sec. The diameter of particle corresponding to the velocity is calculated to be 5, while only about 10 % of the nuclides can be collected on filter paper with a pore size of 0.5. It is supposed that the nuclides exist in particulate materials which is changeable in size. This suggestion is supported from the following evidences. (1) The directly observed behavior of marine snow and the size distribution of particles observed with a coulter counter. (2) The existence of many chemical elements of which residence time is about 150 years. (3) Their possible existence as eutectic solid phases in the seawater. (4) The consistency of the observed accumulation rate of pelagic sediments with that estimated from the settling velocity. (5) The consistency of the decomposition rate of organic matter in the deep water estimated from the oxygen comsumption with that from the settling velocity. 相似文献
76.
A method is described for the determination of Th isotopes (232Th,230Th,228Th and227Th) in seawater through analysis of Th adsorbed on MnO2-impregnated fiber that has been moored in the deep sea for up to 10 months. Since the MnO2-fiber adsorbs Th from seawater at a constant rate, natural234Th can be used as a yield monitor by making a correction for its decay during the period of deployment. The results obtained by the method showed good reproducibility and accuracy. The method has the advantage over the chemical coprecipitation method that the time and labor for sampling and processing a large-volume of seawater is reduced. 相似文献
77.
Using the moored MnO2-fiber method, we have obtained 38 determinations of Th and Pa isotope concentrations from 18 sites along the margin of the western North Pacific near Japan, from water depths of 1,330 to 5,873 m. From our data, we are able to show that (1)228Ra and227Ac are being supplied to the seawater from the slope sediments of Honshu, Japan, (2) our230Th and231Pa concentrations match those obtained byin situ pumping with a MnO2-fiber adsorber in the Japan and Izu-Ogasawara trenches but are significantly higher than those from the Panama and Guatemala basins, and (3) our232Th concentrations show a similar systematic decrease with depth as do those of trace metals like Mn, Al, Te and Bi whose concentrations are strongly controlled by particulate matter scavenging.In contrast, our data fail to show (1) that enhanced removal of230Th and231Pa by scavenging from the water column is taking place near the western margins and (2) that231Pa is being removed in preference to230Th from the water column to the marginal sediments. This is probably due to rapid mixing of the deep waters as compared to the scavenging rates of230Th and231Pa in the water column and at the sediment/seawater interface. 相似文献
78.
Hodaka Kawahata Mayuri Inoue Masato Nohara Atsushi Suzuki 《Journal of Oceanography》2006,62(4):405-412
The δ18O, δ13C and trace element composition of pearls collected from Ago Bay, Japan, were investigated in order to evaluate biomineralization
in the cultured pearl oyster (Pinctada fucata martensii). The oxygen isotopic data suggest that the pearls were produced around 23–24°C, mainly in June to early July, which is consistent
with their occurrence in the field. Therefore the pearls were produced under or close to isotopic equilibrium conditions,
although they showed high calcification rates (higher than 0.2–1.0 g cm− 2yr−1) under which, for example, coral skeletons (calcification rate ∼0.28 g cm− 2yr−1) often show non-equilibrium isotope partitioning. The δ13C values were ∼− 2.9‰ lower than those calculated for offshore waters under equilibrium conditions. This may be due to low-δ13C bottom waters resulting from the degradation of organic matter (OM) or to a contribution of low-δ 13C food. In the latter case, a simple mass balance calculation gives a respiration component of 14%. Twelve trace elements
of bulk pearl samples were classified into four groups on the basis of their enrichment/depletion patterns relative to seawater
and inter-element relationships: group 1, Co, Cr, Pb; group 2, Ba, Cs, U; group 3, Cu, Sn, V, and group 4, Mn, Rb, Mo. Comparison
with coral skeletons suggests that Ba and Mn (groups 2 and 4) were definitely much enriched in proteinaceous OM relative to
aragonite crystals in pearls and that V (group 3) in pearls showed only slight enrichment in the organicrich layer. By contrast,
the other elements showed small differences between both layers (enrichment factor of <3), suggesting that these elements
occur largely in aragonite crystals. 相似文献
79.
Daisuke Tsumune Jun Nishioka Akifumi Shimamoto Shigenobu Takeda Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):111
The first iron (Fe) – fertilization experiment in the western North Pacific was carried out using SF6 to trace the Fe-fertilized water mass. A solution in 10,800 liters of seawater of 350 kg of Fe and 0.48 M of SF6 tracer was released into the mixed layer over a 8 × 10 km area. On the first underway transects through the patch after the Fe release, we observed a significant increase of dissolved Fe (ave. 2.89 nM). The fertilized patch was traced for 14 days by on-board SF6 analysis. A Lagrangian frame of reference was maintained by the use of a drogued GPS buoy released at the center of the patch. The patch moved westward at a rate of 6.8 km d−1. Mixed layer depth increased from 8.5 to 15 m during the experiment. Horizontal diffusivity was determined by the change of SF6 concentration in the patch. The horizontal diffusivity increased during the experiment. We evaluate here the fate of Fe in a Fe-fertilized patch using the dilution rate determined from sulphur hexafluoride (SF6) concentration. Dissolved Fe concentrations subsequently decreased rapidly to 0.15 nM on Day 13. However, the dissolved Fe half-life of 43 h was relatively longer than in previous Fe-enrichment studies, and we observed a larger increase of the centric diatom standing stock and corresponding drawdown of macro-nutrients and carbon dioxide than in the previous studies. The most important reason for the larger response was the phytoplankton species in the western North Pacific. In addition, the smaller diffusivity and shallower mixed layer were effective to sustain the higher dissolved Fe concentration compared to previous experiments. This might be one reason for the larger response of diatoms in SEEDS. 相似文献
80.
The relationship between form drag and the zonal mean velocity of steady states is investigated in a very simple system; a barotropic quasi-geostrophic β channel with sinusoidal topography. When a steady solution is calculated by the modified Marquardt method, keeping the zonal mean velocity constant as a parameter, the characteristic of the solution changes at a phase speed of a wave with a wavenumber higher than that of the bottom topography. For velocities smaller than this critical value, there exists a stable quasi-linear solution similar to the linear solution. For larger velocities, there exist three solutions whose form drag is very large. In addition, the resonant velocity of the mode, whose wavenumber is the same as the bottom topography, has no effect on these solutions. When the quiescent fluid is accelerated by a constant wind stress, acceleration stops around the critical velocity for a wide range of the wind stress. If the wind stress is too large for the acceleration to stop, the zonal current speed continues to increase infinitely. It is implied that the zonal velocity of equilibrium is mainly determined, not by the wind stress, but by the amplitude of the bottom topography and the viscosity coefficient. 相似文献