Decadal seesaw of the Central and Subtropical Mode Water formation associated with the Kuroshio Extension variability   总被引：1，自引：1，他引：0  

Eitarou?OkaEmail author  Bo?Qiu  Shinya?Kouketsu  Kazuyuki?Uehara  Toshio?Suga 《Journal of Oceanography》2012,68(2):355-360

Available Argo profiling float data from 2002 to 2011 were analyzed to examine the effect of the Kuroshio Extension (KE) current system variability on the formation of the Central Mode Water. Just north of the upstream portion of the KE at 140–152°E, formation of a lighter variety of the Central Mode Water in winter was active during the unstable period of the upstream KE in 2006–2009 and was reduced when the upstream KE was in the stable period of 2002–2005 and 2010–2011. This decadal formation variability is out of phase with that of the Subtropical Mode Water just south of the KE.  相似文献   

Holocene paleolimnological changes in Lake Skallen Oike in the Syowa Station area of Antarctica inferred from organic components in a sediment core (Sk4C-02)     

Genki I. Matsumoto  Yukinori Tani  Koji Seto  Tomoko Tazawa  Masumi Yamamuro  Takahiro Watanabe  Toshio Nakamura  Tetsuo Takemura  Satoshi Imura  Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693

Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen, and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm) overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca. 7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year. Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms. During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface, ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher than during the coastal marine period.  相似文献   

Late Pleistocene and Holocene vegetation and climate records from Lake Kotokel, central Baikal region     

Koji Shichi  Hikaru Takahara  Sergey K. Krivonogov  Elena V. Bezrukova  Kenji Kashiwaya  Akihide Takehara  Toshio Nakamura 《Quaternary International》2009,205(1-2):98

Climatically driven Late Pleistocene and Holocene vegetation changes were reconstructed based on pollen records from the sediments of Lake Kotokel and Cheremushka Bog, located on the eastern shore of Lake Baikal. The described paleoenvironmental record has higher resolution than records collected from Lake Baikal and unites individual events identified in prior studies of bottom and onshore cores. Remarkable shifts in landscapes and expansions of index plants are as follows. Forest tundra and/or forest steppe landscape with birch, spruce, Artemisia, and Poaceae prevailed at ca. 50–25 ¹⁴C kyr BP. Tundra and/or steppe vegetation dominated by Artemisia and Poaceae was typical for the Last Glacial Maximum. The expansion of shrub birch and willow occurred at ca. 15.5 ¹⁴C kyr BP. Two peaks of spruce expansion at ca. 47.5–42.4 ¹⁴C kyr BP (Karginian time) and at ca. 14.5–13 ka (Bølling-Allerød warm intervals) suggest that the condition were more humid than today. A slight increase in Artemisia at ca. 11–10.5 ¹⁴C kyr BP (13–12 ka) was indicative of the Younger Dryas event. An expansion of birch forests with fir at ca. 12–6.4 ka suggests higher humidity. The currently dominant Scots and Siberian pine forests with birch expanded since 6.4 ka.  相似文献   

High-<Emphasis Type="Italic">P</Emphasis>, <Emphasis Type="Italic">T</Emphasis> phase relations in the NaAlSi<Subscript>2</Subscript>O<Subscript>6</Subscript> system from first principles computation     

Kenji?KawaiEmail author  Taku?Tsuchiya 《Physics and Chemistry of Minerals》2012,39(4):305-310

Vibrational density of states of the NaAlSi₂O₆ jadeite and NaAlSiO₄ calcium ferrite (CF)-type, and SiO₂ stishovite is calculated as a function of pressure up to 50 GPa using density functional perturbation theory. The calculated frequencies are used to determine the thermal contribution to the Helmholtz free energy within the quasi-harmonic approximation and to derive the equation of state and several thermodynamic properties of interest. A dissociation of jadeite into a mixture of a CF-type phase and stishovite is predicted to occur at 23.4 GPa and 1,800 K with a positive Clapeyron slope of 2.8 MPa/K. Elastic anisotropy for jadeite, the CF-type phase, and stishovite also computed clearly shows that stishovite and the CF-type phase are the most anisotropic and isotropic in these three phases, respectively.  相似文献   

Groundwater flow system in Bengal Delta,Bangladesh revealed by environmental isotopes     

Ratan K. Majumder  M. A. Halim  B. B. Saha  Reo Ikawa  Toshio Nakamura  Makoto Kagabu  Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352

A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers, Bangladesh using environmental isotope (²H, ¹⁸O, ¹³C, ³H, and ¹⁴C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ²H = 7.7 δ¹⁸O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ¹⁸O and δ²H). The δ¹⁸O and δ²H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU, which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of ¹⁴C activity is associated with the heavier δ¹³C values, which indicates the presence of geochemical reactions affecting the ¹⁴C concentration along the groundwater flow system. Both vertical and lateral decrease of ¹⁴C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the Bengal Delta aquifers, Bangladesh.  相似文献   

时域反射仪在监测青藏高原活动层水分变化过程中的应用   总被引：27，自引：13，他引：14  

王绍令  杨梅学  小池俊雄  赵林 《冰川冻土》2000,22(1):78-84

时域反射仪（ＴＤＲ）是一种利用电磁脉冲方法,根据电磁波在土层中的传播速度测试不同土层 的介电常数,接介电常数值可获不同土类在冻融状态下的未冻水含量和总体积含水量．ＴＤＲ仪可在 野外环境下无破损地测得融土和冻土的液态水含量,尤其是能测出不同负温下冻土中未冻水的变 化．该仪器最适用于测量均质细颗粒土的体积含水量,经与烘干称重法对比,ＴＤＲ仪应用在青藏高 原上不同融土类所测含水量值的误差范围：粉土和细砂为±２．５％,粘土和亚粘土为±３．０％,砂砾石 土和碎石土为±５％．经过反复的野外实践证明,用 ＴＤＲ仪测上层含水量具有简便、快速及稳定等 优点,是值得推广的方法．根据青藏公路沿线８个场地埋置的ＴＤＲ仪和地温仪所获的一个年周期的 水、热资料（１９９７．８～１９９８．７）,分析了高原活动层在冻融过程中温度场和水分场的耦合所导致的水分迁移及水分场重分布的规律  相似文献   

Time evolution of galactic warps in prolate haloes     

M. Ideta  S. Hozumi  T. Tsuchiya  M. Takizawa 《Monthly notices of the Royal Astronomical Society》2000,311(4):733-740

A recent observation with the Hipparcos satellite and some numerical simulations imply that the interaction between an oblate halo and a disc is inappropriate for the persistence of galactic warps. Following on from this , we have compared the time evolution of galactic warps in a prolate halo with that in an oblate halo. The haloes were approximated as fixed potentials, while the discs were represented by N -body particles. We have found that the warping in the oblate halo continues to wind up, and finally disappears. On the other hand, for the prolate halo model, the precession rate of the outer disc increases when the precession of the outer disc recedes from that of the inner disc, and vice versa. Consequently, the warping in the prolate halo persisted to the end of the simulation by retaining the alignment of the line of nodes of the warped disc. Therefore, our results suggest that prolate haloes could sustain galactic warps. The physical mechanism of the persistence of warp is discussed on the basis of the torque between a halo and a disc and that between the inner and outer regions of the disc.  相似文献   

Test of the extrapolation method for the numerical integration of the Keplerian motion     

Toshio Fukushima 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):73-76

Two extrapolation methods (Gragg's method and GBS method) were tested for the numerical integration of the Keplerian motion. The tests cleared that the Gragg's method is better for the orbit computation and is 1) easy to control, 2) highly accurate, 3) tough, 4) economic, and 5) very flexible against the close encounter.  相似文献   

Possible observational evidence for the θ⁻² angular distribution of the opening half-angle of gamma-ray burst jets     

Daisuke Yonetoku  Ryo Yamazaki  Takashi Nakamura  Toshio Murakami 《Monthly notices of the Royal Astronomical Society》2005,362(3):1114-1118

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Hydrothermal spinel,corundum and diaspore in lower oceanic crustal troctolites from the Hess Deep Rift     

Toshio Nozaka  Romain Meyer  Robert P. Wintsch  Bryan Wathen 《Contributions to Mineralogy and Petrology》2016,171(6):53

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