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101.
Rare earth element (REE) concentrations in the carbonate lattice of four species of coral have been analyzed and compared with the dissolved REE in ambient seawaters. The corals were from two areas of different salinity, marine (34-34.5) and bay (33-34). The measurement of REE in coral was carried out with inductively coupled plasma mass spectrometry (ICP-MS) after meticulous washing of coral samples, digestion with acetic acid and preconcentration of REE. The concentrations of REE in the two ambient seawaters were quite different, being ten-times higher in the bay area and enriched in light REE. However, the average distribution coefficients (D’s) were almost identical in the two areas. Substantial distribution coefficient differences were observed among the four coral species and the magnitude of inter-species variation in D was also species-dependent. Theoretical calculations imply that pH variation could cause variations in D large enough to account for the small differences between the two areas. 相似文献
102.
Thrusts, pinch-and-swell structures and undulations are present within a 2-m-thick layered shale bed of Miocene age that is overlain by a rhyolite subaqueous pyroclastic flow deposit 2–3 m thick. The deformation structures were caused by loading and lateral compression by the subaqueous pyroclastic flow, probably analogous to those observed in layered muds deformed by a sand mass advancing across them. Prominent thrusts strike east-west and dip south, and the crests of undulations strike east-west, indicating that the subaqeuous pyroclastic flow moved northward. 相似文献
103.
Yoshisuke Nakano 《Advances in water resources》1983,6(2):71-78
The asymptotic behavior of solutions to the problem of wetting fronts is studied in one-dimensional, horizontal and infinite porous media with the soil-water diffusivity proportional to some power of the water content. The uniqueness of the similarity solution for the problem is studied and the properties of this solution are presented. It is shown that the similarity solution is an asymptotic solution of a wide class of initial value problems of wetting fronts in the media. The use of the similarity solution is discussed for the experimental determination of the soil-water diffusivity. 相似文献
104.
Ziqian Wang Kenichi Nakano Eri Ito Hiroshi Kawase Shinichi Matsushima 《地震工程与结构动力学》2023,52(1):128-146
Under hypothetical and idealized conditions, the horizontal site amplification factor (HSAF) is defined as the ratio of the horizontal Fourier amplitude spectrum (FAS) at a point on the Earth's surface with respect to the horizontal FAS at the identical location but on the outcropping seismological bedrock. The HSAF reflects the profile of local sedimentary soils and weathered rock formations, indicating site effects. In most cases, such an idealized HSAF is difficult to measure directly. Thus, quantitatively estimating a HSAF value is a crucial task in strong-motion prediction over the last century. Fortunately, many strong-motion stations have been constructed throughout Japan, facilitating the characterization of HSAFs down to seismological bedrock at more than 1600 observational sites by the generalized inversion technique (GIT). First, this study reported the similarity distribution of the HSAF and the horizontal-to-vertical spectral ratio of earthquakes (HVSRE). Subsequently, we proposed a hybrid method from a novel aspect for estimating HSAF in terms of the observed similarity distribution and the vertical amplification correction function (VACF) proposed previously. Compared with the direct use of HVSRE for substituting HSAF, the hybrid method proposed herein demonstrated an improvement of greater than 30% in terms of the residuals between estimated HSAFs and those separated from observations. 相似文献
105.
Effects of the seasonal variation in thermohaline and wind forcing on the abyssal circulation are investigated by using an
ocean general circulation model. To isolate effects of the seasonality in the thermohaline forcing from those in the wind
forcing, we carry out three experiments with (1) annual-mean wind forcing and perpetual-winter thermohaline forcing, (2) annual-mean
wind forcing and seasonal thermohaline forcing, and (3) seasonal wind forcing and seasonal thermohaline forcing. The deep
water under the seasonal thermohaline forcing becomes warmer than under the perpetual-winter thermohaline forcing. Although
the perpetual-winter thermohaline forcing is widely used and believed to reproduce the deep water better than the annual-mean
forcing, the difference between the results of the perpetual-winter and the seasonal thermohaline forcing is significant.
The seasonal variation of the Ekman convergence and divergence produces meridional overturning cells extending to the bottom
because the period of seasonal cycle is shorter than the adjustment timescale by baroclinic Rossby waves. The heat transport
owing to those Ekman flows and temperature anomalies makes the upper water (0–200 m) colder at low to mid-latitudes (40S–40N)
and warmer at high latitudes. Also the deep water becomes warmer owing to the warming of the northern North Atlantic, the
main source region of North Atlantic Deep Water. The model is also synchronously (i.e., without acceleration) integrated with
seasonal forcing for 5400 y. A past study suggested that under seasonal forcing, a sufficient equilibrium state can be achieved
after only decades of synchronous integration following more than 10 000 y of accelerated integration. Here, the result so
obtained is compared with that of the 5400-y synchronous integration. The difference in the global average temperature is
as small as 0.12 °C, and most of the difference is confined to the Southern Ocean.
Received: 1 May 1998 / Accepted: 5 January 1999 相似文献
106.
How the role of vertical turbulent mixing (VTM) in sea surface cooling (SSC) varies with the moving speed of a tropical cyclone
was examined for Typhoon Rex (1998) by using the Meteorological Research Institute Community Ocean Model (MRI.COM). The MRI.COM
well reproduced TRMM/TMI three-day mean sea surface temperature (SST) fields along Rex’s track. During the fast-moving phase
of Rex, SSC simulated by the MRI.COM was caused by shear-induced VTM on the right side of the track. During the slowly-moving
phase, on the other hand, the Ekman-pumping area mostly overlapped the VTM area right behind Rex’s center. During the recurvature
phase, cool water transported by the upwelling was more efficiently entrained into a mixed layer by the VTM for nearly a 1
near-inertial period after the passage of Rex. We then modified the entrainment formulation of Deardorff (1983), which was
incorporated into a slab mixed-layer ocean model (SOM) so as to fit to the results simulated by the MRI.COM. The principal
modifications are as follows: (1) consideration of turbulent kinetic energy (TKE) production caused by surface wave breaking;
(2) increase in the coefficient for estimating dissipation to balance with TKE production due to turbulent transport; and
(3) changing the initial guess for the critical Richardson number. These modifications led to an improvement of SST simulations
by the SOM. The impact of the modifications on simulated SSTs turned out to be more significant than the impacts of initial
mixed-layer depth and the difference between diurnally-varying and daily mean short-wave radiation. 相似文献
107.
Seasonal changes in oceanographic conditions related to primary productivity was investigated in the southwestern Okhotsk
Sea during non-iced seasons, using the observation data conducted in 2000∼2006. Based on hydrographic characteristics, the
studied area could be classified into two regions, the Coastal Region which is influenced under the Soya Warm Current and
the Forerunner Water of the Soya Warm Current, and the Offshore Region where the Intermediate Cold Water was located in the
subsurface layer. This study is the first report on seasonal change of nutrient and chlorophyll a concentrations in the offshore region of the southwestern Okhotsk Sea. Variability of concentrations of chlorophyll a and nutrients is temporally and regionally high in the Coastal Region. The maximum chlorophyll a concentration in April was observed at the surface layer of both regions. The most remarkable feature on the vertical structure
in the Offshore Region was the consistent existence of the Intermediate Cold Water and the development of seasonal thermocline
in the subsurface layer during summer and autumn. The stratification formed within the euphotic zone in the Offshore Region
resulted in the formation of the subsurface chlorophyll a maximum (SCM) from May to October. Throughout the research period, although less amplitude of nutrients at the surface was
observed in the Coastal Region than that in the Offshore Region, comparable amplitude of chlorophyll a concentration was observed between regions. These results suggested differences of environmental conditions for primary production
between the two regions. Depending on the presence of SCM, relationships between chlorophyll a concentration at the sea surface and chlorophyll a standing stock within the euphotic layer were different. At most stations with SCM, the surface chlorophyll a concentration was lower than 0.6 mg m-3. This suggests that the presence of SCM and the chlorophyll a standing stock within the euphotic layer may be estimated using the surface chlorophyll a concentration from spring to autumn in the studied area. 相似文献
108.
Application of a coprecipitation method combined with low-background γ-spectrometry allowed the isolation of 7Be, 137Cs, 210Pb, and radium and thorium isotopes together with BaSO4, Fe(OH)3, or AMP/Cs in 18 L of coastal water. This simple method showed high chemical yields of 77–91% (mean, 85%) for 210Pb and radium isotopes, 87–92% (mean, 91%) for 7Be and thorium isotopes, and 98% for 137Cs. The activity of the nuclides showed good reproducibility with standard deviations of 1–8%, while the deviation of activity
in particle-reactive 210Pb (32%) and 7Be (21%) in filtered water samples was exceptionally large. 相似文献
109.
Hideyuki Kamaya 《Astrophysics and Space Science》2011,334(2):261-265
Recent observational studies have discovered very small dwarf spheroidal galaxies (dSphs) which are the faintest member of
the local group of galaxies. This paper examines their faintness because of the following reason: Comparing their M/L (mass-luminosity ratio) to that of the other normal dSphs, we find very small dSphs are faint for their dark matter mass.
This indicates their star formation is suppressed. There are two possibilities for the suppression: (1) ram pressure of IGM
(intra-group medium), (2) wind from the Milky Way (MW). Owing to the ram pressure, interstellar medium of very small dSphs
is possible to be stripped because of the shallowness of their gravitational potential. That is, star formation can be terminated
during their evolution. However, the latter is difficult at the moment since their distance is far from MW. The author suggests
star formation was terminated only when very small dSphs were beside MW whose wind was strong. 相似文献