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1.
Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (10Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric 10Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric 10Be events to be derived from the deposition of 10Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric 10Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   
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The temperature distribution at depth is a key variable when assessing the potential of a supercritical geothermal resource as well as a conventional geothermal resource. Data-driven estimation by a machine-learning approach is a promising way to estimate temperature distributions at depth in geothermal fields. In this study, we developed two methodologies—one based on Bayesian estimation and the other on neural networks—to estimate temperature distributions in geothermal fields. These methodologies can be used to supplement existing temperature logs, by estimating temperature distributions in unexplored regions of the subsurface, based on electrical resistivity data, observed geological/mineralogical boundaries, and microseismic observations. We evaluated the accuracy and characteristics of these methodologies using a numerical model of the Kakkonda geothermal field, Japan, where a temperature above 500 °C was observed below a depth of about 3.7 km. When using geological and geophysical knowledge as prior information for the machine learning methods, the results demonstrate that the approaches can provide subsurface temperature estimates that are consistent with the temperature distribution given by the numerical model. Using a numerical model as a benchmark helps to understand the characteristics of the machine learning approaches and may help to identify ways of improving these methods.

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Fukushima  Yo  Higo  Yosuke  Matsushima  Takashi  Otake  Yu 《Acta Geotechnica》2021,16(9):2693-2711
Acta Geotechnica - Liquid bridges in unsaturated soils attach to grain contacts and contribute to strengthening microscopic bonding forces, which leads to macroscopic high strength and stiffness...  相似文献   
5.
Extreme stream-flow events of Citarum River are derived from the daily stream-flows at the Nanjung gauge station. Those events are identified based on their persistently extreme flows for 6 or more days during boreal fall when the seasonal mean stream-flow starts peaking-up from the lowest seasonal flows of June–August. Most of the extreme events of high-streamflows were related to La Ni?a conditions of tropical Pacific. A few of them were also associated with the negative phases of IOD and the newly identified El Ni?o Modoki. Unlike the cases of extreme high streamflows, extreme low streamflow events are seen to be associated with the positive IODs. Nevertheless, it was also found that the low-stream-flow events related to positive IOD events were also associated with El Ni?o events except for one independent event of 1977. Because the occurrence season coincides the peak season of IOD, not only the picked extreme events are seen to fall under the IOD seasons but also there exists a statistically significant correlation of 0.51 between the seasonal IOD index and the seasonal streamflows. There also exists a significant lag correlation when IOD of June–August season leads the streamflows of September–November. A significant but lower correlation coefficient (0.39) is also found between the seasonal streamflow and El Ni?o for September–November season only.  相似文献   
6.
Abstract– We investigated three‐dimensional structures of comet Wild 2 coma particle impact tracks using synchrotron radiation (SR) X‐ray microtomography at SPring‐8 to elucidate the nature of comet Wild 2 coma dust particles captured in aerogel by understanding the capture process. All tracks have a similar entrance morphology, indicating a common track formation process near the entrance by impact shock propagation irrespective of impactor materials. Distributions of elements along the tracks were simultaneously measured using SR‐XRF. Iron is distributed throughout the tracks, but it tends to concentrate in the terminal grains and at the bottoms of bulbs. Based on these results, we propose an impact track formation process. We estimate the densities of cometary dust particles based on the hypothesis that the kinetic energy of impacting dust particles is proportional to the track volume. The density of 148 cometary dust particles we investigated ranges from 0.80 to 5.96 g cm?3 with an average of 1.01 (±0.25) g cm?3. Moreover, we suggest that less fragile crystalline particles account for approximately 5 vol% (20 wt%) of impacting particles. This value of crystalline particles corresponds to that of chondrules and CAIs, which were transported from the inner region of the solar system to the outer comet‐forming region. Our results also suggest the presence of volatile components, such as organic material and perhaps ice, in some bulbous tracks (type‐C).  相似文献   
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The Kuroshio, one of the most energetic western boundary currents in the world, shows variations in its mesoscale features and recirculation gyres, providing an excellent test case of interactions between the mesoscale field and Kuroshio Extension (KE) states. A three-layer quasi-geostrophic model was used to reconstruct flow fields continuous in time and the horizontal plane from the TOPEX/POSEIDON altimeter data based on the variational method. Compared with the solutions obtained by the nudging method, the present results proved that the variational solution was closer to the real field. In the assimilation period, 1993–1997, the baroclinic instability index (BII) was defined to be the phase shift from the uppermost layer to the lowest layer with mesoscale features. In the first half of the assimilation period, the KE took the transition from the elongated to contracted states, in which BII decreased gradually, as a consequence of the KE state shift. In the second half period, BII increased in the downstream region just west of the Shatsky Rise, in which baroclinic instability contributed to the final stage of the contracted state, and was followed by rapidly weakened instability as a trigger of the opposite transition from the contracted to elongated states. The wind-driven recirculation gyre played an active role on the KE transition in the first half period, although not in the second half.  相似文献   
8.
Yosuke Maeda 《Geoforum》2012,43(2):342-352
The recent development of the third sector and the government encouragement of it have attracted the attention of many researchers. In particular, geographical research has examined how the third sector has been affected or changed by government policies or guidelines in recent political economic contexts, especially neo-liberalism and also neo-communitarianism. While much research has demonstrated that the relationship between the government and the third sector is becoming closer, and has considered the problematic impact on the sector or the community, recent studies have described a much more complicated relationship and its consequence. In response, this paper attempts to explore alternative effects of government encouragement at the local community level, through utilising empirical data on recent voluntary activity regarding community safety by the Voluntary Organisations for Crime Prevention Patrol (VOCPP) in Musashino City, a suburb of Tokyo in Japan. Before focusing on the case study in Musashino, the paper briefly outlines key geographical literature on the third sector, and also examines recent expectations of Japan’s third sector using Japanese political documents. Finally, the paper argues that the encouragement of government in fact has the potential to work as a ‘catalyst’ leading to a more independent third sector, with a geographically and organisationally less hierarchical structure, and may also assist in developing a more diversified community.  相似文献   
9.
It is important to estimate hard-to-observe parameters in the ocean interior from easy-to-observe parameters. This study therefore demostrates a reconstruction of observed temperature and salinity profiles of the sea east of Japan (30°≈40°N, 140°≈150°E). The reconstruction was done by estimating suboptimal state from several values of the observed profiles and/or sea surface dynamic height (SDH) calculated from the profiles. The estimation used a variational method with vertical coupled temperature-salinity empirical orthogonal function (EOF) modes. Profiles of temperature and salinity in the subtropical region are effectively reconstructed from in situ temperature profile data, or sea surface temperature (SST) and SDH. For example, the analyzed temperature field from SST and SDH has an accuracy to within 1°C in the subtropical region. Salinity in the sea north of Kuroshio, however, is difficult to estimate because of its complex variability which is less correlated with temperature than in the subtropical region. Sea surface salinity is useful to estimate the subsurface structure. We also show the possibility that the estimation is improved by considering nonlinearity in the equation calculating SDH from temperature and salinity analysis values in order to examine the misfit between analysis and observation. Analysis using TOPEX/POSEIDON altimetry data instead of SDH was also performed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
10.
I present the derivation of the Preconditioned Optimizing Utility for Large-dimensional analyses (POpULar), which is developed for adopting a non-diagonal background error covariance matrix in nonlinear variational analyses (i.e., analyses employing a non-quadratic cost function). POpULar is based on the idea of a linear preconditioned conjugate gradient method widely adopted in ocean data assimilation systems. POpULar uses the background error covariance matrix as a preconditioner without any decomposition of the matrix. This preconditioning accelerates the convergence. Moreover, the inverse of the matrix is not required. POpULar therefore allows us easily to handle the correlations among deviations of control variables (i.e., the variables which will be analyzed) from their background in nonlinear problems. In order to demonstrate the usefulness of POpULar, we illustrate two effects which are often neglected in studies of ocean data assimilation before. One is the effect of correlations among the deviations of control variables in an adjoint analysis. The other is the nonlinear effect of sea surface dynamic height calculation required when sea surface height observation is employed in a three-dimensional ocean analysis. As the results, these effects are not so small to neglect.  相似文献   
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