排序方式： 共有29条查询结果，搜索用时 305 毫秒
1.
Recovery of thermohaline circulation under CO2 stabilization and overshoot scenarios 总被引：1，自引：0，他引：1
Norikazu. Nakashiki Dong-Hoon Kim Frank O. Bryan Yoshikatsu Yoshida Daisuke Tsumune Koki Maruyama Hideyuki Kitabata 《Ocean Modelling》2006,15(3-4):200
In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO2 stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO2 levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries. 相似文献
2.
Koki Midorikawa 《Journal of Oceanography》1977,33(6):311-319
Internal waves were observed by measuring temperature variations of several subsurface layers at the innermost part of Suruga Bay from December 1968 to October 1971. Spectral energy densities of temperature fluctuations were computed from the records of the measurements. In the shorter period range from one minute to one hour, peaks of energy density were found occasionally in the range shorter than the minimum of VÄisÄlÄ periods computed from the vertical distribution of water density. It has been generally understood, however, that the periods of internal waves in a stable stratum should be within the range between the inertial and VÄisÄlÄ periods.The measurements of tidal currents in the surface and lower layers, which were undertaken simultaneously with the temperature measurements, revealed that the short-period oscillations were associated with the increase of current velocity and of vertical shear of current at the pycnocline.It is considered that observed periods shorter than the minimum of VÄisÄlÄ period are not real but apparent periods due to the Doppler effect, because the waves are generated in the velocity shear of tidal current and the source is moving towards the station with the tidal current. 相似文献
3.
Shaking during the 1995 Kobe earthquake caused surface material to be more mobile in catchment areas in the Rokko Mountains, Kobe, where there are some active fault lines. As a result, there were many landslides associated with the earthquake. The sedimentation rate in a pond in the mountains increased several fold, then exponentially decreased with seasonality over several years. Six years after the earthquake there were no marked surface movements related to the earthquake, even though the sedimentation rates had increased slightly. A new steady state for the structure of the earthquake‐modi?ed surface had evidently been reached. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
5.
Kenji Kashiwaya Hideo Sakai Masayuki Ryugo Masae Horii Takayoshi Kawai 《Journal of Paleolimnology》2001,25(3):271-278
Analysis of physical properties in long sediment cores (BDP96) from Academician Ridge in Lake Baikal indicates that major climato-limnological changes during the past 3.5 Myr occurred at about 2.5–2.8, 1.7–1.9, and 0.9–1.2 Ma, which were close to times of major geomagnetic polarity reversals (Matuyama/Gauss, Olduvai, Jaramillo + Matuyama/Brunhes). The principal climato-limnological oscillation has a long-term period of nearly 1,000 kyr, which corresponds to the periodicity of fluctuation in solar insolation. It also seems to be related to geomagnetic field intensity. Other long-term period of 400 kyr corresponds to Milankovitch parameters of eccentricity. These results suggest that changes in solar insolation were closely related to long-term environmental variations in the deep continental interior. 相似文献
6.
Kenji Kashiwaya Masayuki Ryugo Masae Horii Hideo Sakai Toshio Nakamura Takayoshi Kawai 《Journal of Paleolimnology》1999,21(2):143-150
The St.16 core obtained from the Academician Ridge of Lake Baikal in eastern Siberia may span about 260 000 years, and some physical properties of the core samples are closely related to aquatic paleoproductivity and climatic change. The median of grain size, grain density, and water content fluctuate synchronously. They also are connected with change in the abundance of biogenic silica (diatoms). The physical parameters indicate that there were high aquatic productivity periods around interglacial periods (MIS 5 and 7; 70 000-125 000 yr B.P. and 180 000-250 000 yr B.P.). Comparatively large clastics were transported from outside of the lake through various routes (ice rafting, etc.) in addition to fluvial routes during the glacials or 'stadials. There are ca. 20 000 yr, 40 000 yr and 100 000 yr periods in the variations of physical properties. These are related to the three Milankovitch parameters of solar insolation. 相似文献
7.
日本大沼湖沉积物碳氮比值、有机碳同位素特征及其近400年的古气候环境意义 总被引：1，自引：0，他引：1
通过对日本大沼湖沉积物样品总有机碳含量(TOC)及其稳定同位素、总氮含量(TN)和C/N值的测定,结合沉积岩芯火山灰和1℃年代,分析了大沼湖沉积物中有机质的来源,探讨了沉积物有机碳同位素的主要影响因素.结果表明:大沼湖沉积物中有机质主要来源于自生藻类,受陆源输入的影响较小;沉积物δ13C值指示了夏季温度的变化.过去400年来,大沼湖地区存在1660～ 1730年和1780～ 1860年两个明显的冷期,与邻近地区冰芯、树轮和湖泊沉积物记录的冷期基本一致,分别对应于Maunder和Dalton太阳黑子极小期. 相似文献
8.
Tetsuya Yokoyama Yusuke Ohkuma Keiji Nishikawa Koki Sumiya Ikshu Gautam 《Geostandards and Geoanalytical Research》2023,47(2):415-435
The Cr isotope ratios of terrestrial and extra-terrestrial materials are emerging as one of the most important tracers in geosciences. Previous studies on Cr isotopic measurements using TIMS have found that there is residual Cr isotopic fractionation between the mass-fractionation-corrected 53Cr/52Cr and 54Cr/52Cr ratios, which may cause an offset of obtained ratios from the reference values. The residual fractionation was thought to be caused by the evaporation of Cr-oxide species during thermal ionisation, but the mechanism by which this residual fractionation could be reduced remained unclear. Here we revisit the issue of residual fractionation and propose that this problem can be alleviated by utilising W filaments instead of conventionally used Re filaments for Cr ionisation. Using W filaments, the formation of CrO+ was suppressed during heating as the filament temperature was ~ 100 °C lower than when Re filaments were used. In repeated measurement of a carbonaceous chondrite, the intermediate precisions of 53Cr/52Cr and 54Cr/52Cr ratios in the W filament runs were two to three times better than those of the Re filament runs. Therefore, the new finding of this study will be of key importance for future studies of Cr isotopes for terrestrial and extra-terrestrial materials. 相似文献
9.
Five years of observations on sedimentation rates in two ponds located near transformed land areas in the Kobe district of central Japan have shown the relationship between sedimentation and development during land transformation. One of the ponds observed has artificial land transformation in its drainage area (KR), whereas the other does not (KN). The sedimentation rate in the pond without artificial land transformation is roughly proportional to the rainfall intensity, whereas in the pond with land transformation it is related to change in the transformed area as well as the rainfall intensity. The relative sedimentation rate (sedimentation rate divided by the catchment area and rainfall intensity) is also related to loss on ignition and grain density; large relative sedimentation rates correspond to low loss on ignition and high grain density, suggesting that these factors are very sensitive to land transformation. Changes in catchment factors, which indicate the topographical and hydrological conditions in the catchment area, are inversely proportional to change in the ratio of the reclaimed to the natural area; this is indicative of change in the erodibility of the surface material in the catchment area. © 1997 John Wiley & Sons, Ltd. 相似文献
10.
Wook-Hyun Nahm Gyoo Ho Lee Dong-Yoon Yang Ju-Yong Kim Kenji Kashiwaya Masayoshi Yamamoto Aya Sakaguchi 《Journal of Paleolimnology》2010,43(3):489-498
This paper describes mean grain-size data from the 137Cs- and 210Pb-dated sediment core BS-3 (33-cm long) recovered from Jinheung Pond, located in the southwestern part of the Korean Peninsula.
Grain-size analysis of the Jinheung Pond sediments shows a clear signal for changes in annual precipitation over the past
60 years. Instrumental records of annual precipitation (AP) and the annual summation of the precipitation of >50 mm per day
(AP50), which reflects the energy available for sediment transport, correlate well with the mean grain-size distributions
measured in the core. The most plausible mechanism for this response in mean grain size is variations in the annual amount
and intensity of precipitation. Heavy precipitation enhances soil erosion over the catchment area and increases the transport
capacity of streams and rivers. Thus, coarser mean grain size should reflect higher precipitation, and smaller mean grain
size should reflect lower rainfall. In the data from core BS-3, however, grain-size peaks attributed to increased annual precipitation
are not prominent. This is because a dam prevents removal of fine particles from the pond via the outflow. Therefore, the
mean grain-size value represents somewhat larger sediments together with fine clays. The results of this study show that sediments
of dammed lakes and ponds are well suited for high-resolution environmental investigations, especially for records of changes
in precipitation over time. 相似文献