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171.
Norikazu Kinoshita Yuko Sato Takeyasu Yamagata Hisao Nagai Akihiko Yokoyama Takashi Nakanishi 《Journal of Oceanography》2007,63(5):813-820
In order to estimate the deposition rate of extraterrestrial material onto a manganese crust in a search for supernova debris,
we analyzed the contents of 10Be, 230Th, 231Pa, and 239,240Pu in a sample of manganese crust collected from the North Pacific Ocean. On the basis of the depth profile of 10Be, the growth rate of the manganese crust was determined to be 2.3 mm Myr−1. The uptake rates of 10Be, 230Th, and 231Pa onto the manganese crust were estimated to be 0.22–0.44%, 0.11–0.73%, and 1.4–4.5%, respectively, as compared to the deposition
rates onto the deep-sea sediments near the sampling station, while that for 239,240Pu was 0.14% as compared to the total inventory of seawater and sediment column. Assuming that sinking particles represent
0.11–4.5% of the uptake rates, the deposition rate of extraterrestrial material onto the manganese crust was estimated to
be 2–800 μg cm−2Myr−1 according to the uptake of 10Be onto the manganese crust. Further, our estimate is similar to the value of 9–90 μg cm− 2Myr−1 obtained using the integrated global production rate of 10Be and the deposition rate of 10Be onto the manganese crust. 相似文献
172.
Benedikt Soja Richard S. Gross Claudio Abbondanza Toshio M. Chin Michael B. Heflin Jay W. Parker Xiaoping Wu Tobias Nilsson Susanne Glaser Kyriakos Balidakis Robert Heinkelmann Harald Schuh 《Journal of Geodesy》2018,92(9):1063-1077
The Global Geodetic Observing System requirement for the long-term stability of the International Terrestrial Reference Frame is 0.1 mm/year, motivated by rigorous sea level studies. Furthermore, high-quality station velocities are of great importance for the prediction of future station coordinates, which are fundamental for several geodetic applications. In this study, we investigate the performance of predictions from very long baseline interferometry (VLBI) terrestrial reference frames (TRFs) based on Kalman filtering. The predictions are computed by extrapolating the deterministic part of the coordinate model. As observational data, we used over 4000 VLBI sessions between 1980 and the middle of 2016. In order to study the predictions, we computed VLBI TRF solutions only from the data until the end of 2013. The period of 2014 until 2016.5 was used to validate the predictions of the TRF solutions against the measured VLBI station coordinates. To assess the quality, we computed average WRMS values from the coordinate differences as well as from estimated Helmert transformation parameters, in particular, the scale. We found that the results significantly depend on the level of process noise used in the filter. While larger values of process noise allow the TRF station coordinates to more closely follow the input data (decrease in WRMS of about 45%), the TRF predictions exhibit larger deviations from the VLBI station coordinates after 2014 (WRMS increase of about 15%). On the other hand, lower levels of process noise improve the predictions, making them more similar to those of solutions without process noise. Furthermore, our investigations show that additionally estimating annual signals in the coordinates does not significantly impact the results. Finally, we computed TRF solutions mimicking a potential real-time TRF and found significant improvements over the other investigated solutions, all of which rely on extrapolating the coordinate model for their predictions, with WRMS reductions of almost 50%. 相似文献
173.
This study describes the three-dimensional distributions of the Turner angle (Tu) and the potential vorticity (PV) of the
main pycnocline water in the subtropical North Pacific (10–50°N, 120°E–120°W) using a large in situ CTD data set taken by
the Argo profiling floats during June to October of 2001–2009 to clarify the detailed distribution of the central water and
the mode waters as well as the relationship between these water masses. The ventilated part of the main pycnocline water (σ
θ < 26.7 kg m−3) in the subtropical gyre generally displays a sharp peak in Tu value of 59° in the histogram. The Tu histograms for 10° × 10°
geographical boxes mostly show that the mode for the Tu value is 59° too, but they also show some regional differences, suggesting
some types of relations with the North Pacific mode waters. To further investigate this relationship, the appearance probability
density function of the central water (defined as the main pycnocline water with Tu = 56°–63°) and those of the mode waters
with PVs lower than the critical value on each isopycnal surface were analyzed. The distribution area of the central mode
water (CMW) corresponds so well with that of the central water that a direct contribution of the CMW to the formation and
maintenance of the central water is suggested. On the other hand, the distribution areas of subtropical mode water (STMW),
Eastern STMW, and transition region mode water do not correspond to that of the central water. Nevertheless, indirect contributions
of these mode waters to the formation and maintenance of the central water through salt finger type convection or diapycnal
mixing are suggested. 相似文献
174.
Variations of water properties in surface and intermediate layers along 32°S in the southern Indian Ocean were examined using
a 50-year (1960–2010) time series reproduced from historical hydrographic and Argo data by using optimum interpolation. Salinity
in the 26.7–27.3σθ density layer decreased significantly over the whole section, at a maximum rate of 0.02 decade−1 at 26.8–26.9σθ, for the 50-year average. Three deoxygenating cores were identified east of 75°E, and the increasing rate of apparent oxygen
utilization in the most prominent core (26.9–27.0σθ) exceeded 0.05 ml l−1 decade−1. The pycnostad core of Subantarctic Mode Water (SAMW) and the salinity minimum of Antarctic Intermediate Water shifted slightly
toward the lighter layers. Comparisons with trans-Indian Ocean survey data from 1936 suggest that the tendencies found in
the time series began before 1960. Interestingly, cores of many prominent trends were located just offshore of Australia at
26.7–27.0σθ, which is in the SAMW density range. Spectrum analysis revealed that two oscillation components with time scales of about
40 and 10 years were dominant in the subsurface layers. Our results are fairly consistent with, and thus support, the oceanic
responses in the southern Indian Ocean to anthropogenic climate change predicted by model studies. 相似文献
175.
Toshio Fukushima 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):231-241
This paper reviews three recent works on the numerical methods to integrate ordinary differential equations (ODE), which are
specially designed for parallel, vector, and/or multi-processor-unit(PU) computers. The first is the Picard-Chebyshev method
(Fukushima, 1997a). It obtains a global solution of ODE in the form of Chebyshev polynomial of large (> 1000) degree by applying
the Picard iteration repeatedly. The iteration converges for smooth problems and/or perturbed dynamics. The method runs around
100-1000 times faster in the vector mode than in the scalar mode of a certain computer with vector processors (Fukushima,
1997b). The second is a parallelization of a symplectic integrator (Saha et al., 1997). It regards the implicit midpoint rules
covering thousands of timesteps as large-scale nonlinear equations and solves them by the fixed-point iteration. The method
is applicable to Hamiltonian systems and is expected to lead an acceleration factor of around 50 in parallel computers with
more than 1000 PUs. The last is a parallelization of the extrapolation method (Ito and Fukushima, 1997). It performs trial
integrations in parallel. Also the trial integrations are further accelerated by balancing computational load among PUs by
the technique of folding. The method is all-purpose and achieves an acceleration factor of around 3.5 by using several PUs.
Finally, we give a perspective on the parallelization of some implicit integrators which require multiple corrections in solving
implicit formulas like the implicit Hermitian integrators (Makino and Aarseth, 1992), (Hut et al., 1995) or the implicit symmetric
multistep methods (Fukushima, 1998), (Fukushima, 1999).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
176.
North Pacific Tropical Water: its climatology and temporal changes associated with the climate regime shift in the 1970s 总被引:2,自引:0,他引:2
North Pacific Tropical Water (NPTW) is characterized as a subsurface salinity maximum flowing in the North Equatorial Current and is the main source of salt for the North Pacific. We briefly describe the climatological features of its formation and circulation, and then examine temporal changes in its properties associated with the climate regime shift in the 1970s. We use a variety of data, which include the repeat hydrographic sections along 130°E, 137°E, 144°E and 155°E meridians, the hydrographic data from the Hawaii Ocean Time-series, the World Ocean Atlas 1994, and available gridded data of wind stress and evaporation. The classical idea that NPTW originates from the zone of the highest sea surface salinity at 20°–30°N centered around the international date line and spreads along the isopycnal geostrophic flow patterns is confirmed. Further, it is shown that the meridional extent of NPTW along 137°E is from 10°N to 23°N on average and the highest salinity core lies at about 15°N and 24.0σθ, and that the portion of NPTW north (south) of about 15°N originates from the formation region west (east) of the date line. NPTW in the 137°E section changed remarkably associated with the mid-1970s regime shift. North of 15°N NPTW increased both in its salinity and thickness while to the south of 15°N only its salinity increased and its thickness remained unchanged. The westward geostrophic velocity is increased significantly in both the southern and northern parts of NPTW. The northern thickening and speedup and the southern speedup increased NPTW transport across 137°E. The changes in the thermohaline forcing such as evaporation and Ekman salt convergence in the NPTW formation region possibly contributed to the increases in salinity in the southern part of NPTW, but not to that of the northern part. On the other hand, the increased Ekman pumping accounts for the increase of the NPTW inventory and transport at 137°E. The increased salinity of NPTW at 137°E, especially its northern portion, was presumably caused by an increase in its formation rate rather than changes in the sea surface salinity in its formation region; the thicker the NPTW layer is, the saltier is the core that tends to survive the mixing processes. 相似文献
177.
THE CLIMATE FEATURES OF THE SOUTH CHINA SEA WARM POOL 总被引:1,自引:0,他引:1
There exists a warm pool in the South China Sea (SCS). The temporal and spatial distribution and evolution of SCS warm pool is investigated using water temperatures at a depth of 20 min the sea. The formation of the warm pool is discussed by combining water temperatures with geostrophic currents and simulated oceanic circulation. It is found that there are significant seasonal and interannual changes in the warm pool and in association with the general circulation of the atmosphere. The development of SCS warm pool is also closely related to the gyre activities in the sea and imported warm water from Indian Ocean (Java Sea) besides radiative warming. 相似文献
178.
Salat Jordi Pascual Josep Flexas Mar Chin Toshio Michael Vazquez-Cuervo Jorge 《Ocean Dynamics》2019,69(9):1067-1084
Ocean Dynamics - Marine and atmospheric parameters, including temperature observations from surface to 80 m (at 6 depths) are measured since September 1973 on a higher-than-weekly... 相似文献
179.
Noriko Hasebe Yasuyuki Nakano Hikaru Miyamoto Toshio Higashino Akihiro Tamura Shoji Arai Ju‐Yong Kim 《Island Arc》2016,25(2):111-125
The Hakusan volcano, central Japan, is located in a region where two subducting plates (the Pacific Plate and the Philippine Sea Plate) overlap near the junction of four plates adjacent to the Japanese Islands (the Pacific Plate, the Philippine Sea Plate, the Eurasia Plate, and the North American Plate). The Hakusan volcano consists of products from four major volcanic episodes: Kagamuro, Ko‐hakusan, and Shin‐Hakusan I and II. To date the eruption events of the Hakusan volcano we applied thermoluminescence and fission track methods. 238U(234U)–230Th disequilibrium and 206Pb/238U methods were applied to date the zircon crystallization ages for estimating the magma residence time before the eruptions. The eruption ages we obtained are ca 250 ka for Kagamuro, ca 100 ka and ca 60 ka for Ko‐Hakusan, ca 50 ka for Shin‐Hakusan I, and <10 ka for Shin‐Hakusan II. They are concordant with previous reports based on K–Ar dating. Some of the pyroclastic rocks, possibly originating from Shin‐Hakusan II activities, are dated to be ca 36 ka or 50 ka, and belong to the Shin‐Hakusan I activity. The zircon crystallization ages show several clusters prior to eruption. The magma residence time was estimated for each volcanic activity by comparing the major crystallization events and eruption ages, and we found a gradual decrease from ca. 500 ky for the Kagamuro activity to ca. 5 ky for the Shin‐Hakusan II activity. This decrease in residence time may be responsible for the decrease in volume of erupted material estimated from the current topography of the region. The scale of volcanic activity, which was deduced from the number of crystallized zircons, is more or less constant throughout the Hakusan volcanic activity. Therefore, the decrease in magma residence time is most likely the result of stress field change. 相似文献
180.
The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical mode water (STMW), central mode water (CMW), and eastern subtropical mode water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σθ) range of the lighter STMW (25.0 < σθ < 25.2 kg m−3) and lighter CMW (26.0 < σθ < 26.2 kg m−3), compared to previous estimates. The renewal time of permanent pycnocline water was estimated as the volume of water divided by the subduction rate for each σθ class: 2–4 years for ESTMW (24.5 < σθ < 25.2 kg m−3), 2 years for the lighter STMW (25.0 < σθ < 25.3 kg m−3), 5–9 years for the denser STMW (25.3 < σθ < 25.6 kg m−3), 10–20 years for the lighter CMW (26.0 < σθ < 26.2 kg m−3), 20–30 years for the middle CMW (26.2 < σθ < 26.3 kg m−3), and 60 years or longer for the denser CMW (26.3 < σθ < 26.6 kg m−3). A comparison of the water volume and subduction rate in potential temperature–salinity (θ–S) space indicated that the upper permanent pycnocline water (25.0 < σθ < 26.2 kg m−3) was directly maintained by nondiffusive subduction of winter surface water, including STMW and lighter CMW. The lower permanent pycnocline water (26.2 < σθ < 26.6 kg m−3) may be maintained through the subduction of fresher and colder water from the subarctic–subtropical transition region and subsequent mixing with saltier and warmer water. Diagnosis of the potential vorticity (PV) of the subducted water demonstrated that the low PV of STMW was mainly due to the large subduction rate, whereas that of both ESTMW and CMW was due mainly to the small density advection rate (cross-isopycnal flow). Additionally, a relatively large subduction rate probably contributes to the low PV of part of the lighter CMW (ESTMW) formed in the region around 38°N and 170°W (28°N and 145°W), which is characterized by a relatively thick winter mixed layer and an associated mixed-layer front, causing a large lateral induction rate. 相似文献