Climatic and environmental changes at southeastern coast of Lake Biwa over past 3000 years, inferred from borehole temperature data     

Shusaku Goto  Hideki Hamamoto  Makoto Yamano 《Physics of the Earth and Planetary Interiors》2005,152(4):314-325

In order to infer past climatic change in central Japan, we measured temperatures in a borehole at the Karasuma site, on the southeastern coast of Lake Biwa, and reconstructed sediment surface temperature history during the last 3000 years. The reconstructed temperature history shows apparent Medieval Warm Period, Little Ice Age, and contemporary temperature warming. However, the large amplitude of the temperature changes up to 4-5 K cannot be explained by past climatic change only, suggesting that there was some other cause of the larger amplitude temperature changes. The onsets of temperature decrease in the late 12th century a.d. and temperature increase in the mid 17th century a.d. appear to coincide with occurrences of two destructive earthquakes (1185 and 1662 a.d.) that caused water level changes of Lake Biwa. It suggests that the reconstructed sediment surface temperature history reflects the environmental change due to tectonically induced water level changes of the lake. If the annual mean of the ground surface temperature was higher than that of the bottom water temperature in a shallow part of the lake, which is consistent with the present-day data, the large amplitude of the sediment surface temperature change may be attributed to a combined effect of past climatic and environmental changes. Thus, we suggest that the borehole temperature at the Karasuma site preserves information not only on past climate changes but also on environmental changes due to tectonically induced water level changes.  相似文献   

Long-term monitoring of the temperature profile in a deep borehole: Temperature variations associated with water injection experiments and natural groundwater discharge     

Makoto Yamano  Shusaku Goto 《Physics of the Earth and Planetary Interiors》2005,152(4):326-334

Long-term temperature monitoring was carried out in a borehole drilled for investigation of the Nojima fault, an active fault in SW Japan, using the distributed optical fiber temperature sensing (DTS) technique. Temperatures in the borehole had been measured every 1 m along an optical fiber cable with a resolution of about 0.1 K over a period of 6 years. Water injection experiments were conducted in this borehole in 1997, 2000 and 2003. Monitoring of the temperature profile was started after the first injection experiment, and the temperature profile remained very stable until the start of the second injection experiment. During the second and third experiments, the temperatures in the borehole dropped due to cooling by the injected water but no appreciable temperature change was observed below about 580 m. It clearly shows that the water leaked out of the hole around this point and the leaking depth is estimated to be about 540 m based on the shape of the temperature profile. After the injection was stopped, the recovery of the temperature to the undisturbed profile was exceptionally slow around the leaking point, resulting in a local temperature anomaly, probably because the water leaking out of the hole had cooled the surrounding formations extensively. A very similar temperature anomaly was observed at the beginning of temperature monitoring, which suggests that water leaked out at the same depth in the first injection experiment as well. Between the second and third injection experiments, the top of the borehole was kept open to allow groundwater discharge for about 1 month in 2000 and 2003. In both periods, groundwater flowed out continuously and the shapes of the observed temperature profiles indicate that the groundwater entered in the hole at the same depth as the leaking point during the injection experiments. The temperature records also show that the rate of discharge had been nearly constant through the two test periods. The water discharge appears to have been little affected by the water injection. These results demonstrate that the optical fiber temperature monitoring system is a very effective tool for hydrological experiments.  相似文献   

Evidence for ocean water invasion into the Chicxulub crater at the Cretaceous/Tertiary boundary     

Kazuhisa GOTO  Ryuji TADA  Eiichi TAJIKA  Timothy J. BRALOWER  Takashi HASEGAWA  Takafumi MATSUI 《Meteoritics & planetary science》2004,39(7):1233-1247

Abstract The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.  相似文献   

Optical properties of 4248 IRAS galaxies     

Tomotsugu Goto 《Monthly notices of the Royal Astronomical Society》2005,360(1):322-339

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Radial and 2D colour properties of E+A galaxies   总被引：1，自引：0，他引：1  

Chisato Yamauchi  Tomotsugu Goto 《Monthly notices of the Royal Astronomical Society》2005,359(4):1557-1574

We investigated the radial colour gradient and two-dimensional (2D) colour properties of 22 E+A galaxies with  5.5 < Hδ equivalent width(EW) < 8.5 Å  and 49 normal early-type galaxies as a control sample at a redshift of <0.2 in the Second Data Release of the Sloan Digital Sky Survey. We found that a substantial number of E+A galaxies exhibit positive slopes of radial colour gradient (bluer gradients toward the centre) which are seldom seen in normal early-type galaxies. We found irregular 'colour morphologies'– asymmetrical and clumpy patterns – at the centre of g − r and r − i 2D colour maps of E+A galaxies with positive slopes of colour gradient. Kolomogorov–Smirnov two-sample tests show that g − r and r − i colour gradient distributions of E+A galaxies differ from those of early-type galaxies with a more than 99.99 per cent significance level. We also found a tight correlation between radial colour gradients and colours, and between radial colour gradients and the 4000-Å break in the E+A sample; E+A galaxies which exhibit bluer colour or weaker D ₄₀₀₀ tend to have positive slopes of radial colour gradient. We compared the GISSEL model and E+A observational quantities,  Hδ EW, D ₄₀₀₀  and u − g colour, and found that almost all our E+A galaxies are situated along a single evolutionary track. Therefore, these results are interpreted as E+A galaxies evolving from  Hδ EW ∼ 8 Å  to  Hδ EW ∼ 5 Å  , with colour gradients changing from positive to negative, and with the irregular 2D colour map becoming smoother, during a time-scale of ∼300 Myr. Our results favour the hypothesis that E+A galaxies are post-starburst galaxies caused by merger/interaction, having undergone a centralized violent starburst.  相似文献   

The possibility of inferring paleoseismicity from paleomagnetic dating of speleothems, western Japan   总被引：2，自引：0，他引：2  

Hayao Morinaga  Takafumi Yonezawa  Yasuhisa Adachi  Hiroo Inokuchi  Hiroya Goto  Katsumi Yaskawa 《Tectonophysics》1994,230(3-4):241-248

Paleomagnetic dating of continuously growing stalagmites by comparing their paleomagnetic records with a standard record, has been applied to study the paleoseismic history of a region of western Japan. Three stalagmites (speleothems), which are assumed to have started growing since collapse of the limestone blocks on which they are formed, were collected from two limestone caves located below the Akiyoshi plateau, western Japan. From the paleomagnetic results, it is estimated that they began to grow at 6000, 2500 and 2000 yr B.P., respectively. On the assumption that their growth began immediately after their host limestone blocks fell, these three ages are interpreted to indicate the dates of past earthquakes in this region which triggered the break-off and fall of the blocks. Earthquakes are suggested because many huge collapsed limestone blocks and speleothems are observed in many caves in this region.  相似文献   

Storage-efficient method for generating contours focusing on roundness     

Hiroyuki Goto  Yoichi Shimakawa 《International journal of geographical information science》2016,30(2):200-220

A storage-efficient contour generation method, focusing on planar contours, is developed. Given cartographic elevations on a rectangular lattice, a continuous bivariate function, z = f(x, y), is determined by interpolating the elevation values. Then, we focus on a contour determined by z = constant. The contour curve is partitioned into multiple sections, each of which is exactly or approximately round. Three curvature types are introduced to evaluate the roundness of each section. The area and perimeter of the contour are computed by one-dimensional line integration using Green’s theorem. If the contour is open, it is divided into two curves starting from the same initial point, with the control points advancing in opposite directions. Two types of numerical experiments are performed to validate the effectiveness of the proposed method. One experiment uses an analytically defined elevation function and investigates the number of control points and computation time for a resulting computation error. The second experiment uses actual digital elevation model data of an isolated island in Japan and compares the proposed method with existing ones. Because the algorithm does not require lattice subdivision and the number of control points is drastically reduced, the proposed method is storage efficient.  相似文献   

A monitoring result of polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku during 2012–2014: temporal variation and the relationship with the trophic position     

Naohiko Ohkouchi  H. Shibata  Y. Chikaraishi  H. Nomaki  N. O. Ogawa  T. Nagata  T. Goto  K. Fujikura  H. Kitazato 《Journal of Oceanography》2016,72(4):629-639

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Anomalous Large Scavenging of 230Th and 231Pa Controlled by Particle Composition in the Northwestern North Pacific     

Hisashi Narita  Ryota Abe  Kazuhisa Tate  Young-Ill Kim  Koh Harada  Shizuo Tsunogai 《Journal of Oceanography》2003,59(5):739-750

We report the role of particle composition and lateral particle movement that influences the oceanic distribution of ²³¹Pa and ²³⁰Th. Settling particles were collected during sediment trap experiments. These and surface sediments were obtained from five stations along 38 to 44°N in the northwestern North Pacific. The high total mass flux and seasonal variations in the marginal area of the western North Pacific are controlled by the supply of lithogenic materials and primary productivity. The high content of the lithogenic material in the settling particles in this area contributes to ²³⁰Th_ex fluxes that exceed the local rate of supply. The lithogenic materials are important as a carrier of ²³⁰Th and contribute to the fractionation between ²³⁰Th and ²³¹Pa in the ocean, as the ²³¹Pa_ex/²³⁰Th_ex ratio in the settling particles decreases with increasing ²³²Th concentration. The ²³¹Pa_ex/²³⁰Th_ex ratio in the settling particles collected in the abyssal basin decreases with water depth, which indicates that lateral transport of the lithogenic particles from the marginal area and/or shallower depth plays an important role in determining the ²³¹Pa_ex/²³⁰Th_ex ratio in a population of settling particles and remineralization. This indicates that lateral redistribution of particles and sediment focusing influence the ²³¹Pa_ex/²³⁰Th_ex ratios in surface sediments. Thus, the observations reported here mean that the use of the sediment ²³¹Pa_ex/²³⁰Th_ex ratio as a paleoproductivity proxy will be problematic in the northwestern North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Variations in the thermal conductivities of surface sediments in the Nankai subduction zone off Tokai, central Japan     

Shusaku Goto  Tomonobu Mizoguchi  Ryo Kimura  Masataka Kinoshita  Makoto Yamano  Hideki Hamamoto 《Marine Geophysical Researches》2012,33(3):269-283

We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1?W/m?K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (??1.0?W/m?K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (<0.9?W/m?K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9?W/m?K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features.  相似文献