Interhemispheric anti-phasing of rainfall during the last glacial period   总被引：1，自引：0，他引：1  

Xianfeng Wang  Augusto S. Auler  R. Lawrence Edwards  Hai Cheng  Emi Ito  Maniko Solheid 《Quaternary Science Reviews》2006,25(23-24):3391

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts (<1‰) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere.We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ¹⁸O (wet periods, intense SAM) at our site are synchronous with maxima in δ¹⁸O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor's greenhouse properties.  相似文献   

Alkylbenzenes in mussels from South and South East Asian coasts as a molecular tool to assess sewage impact     

Tsutsumi S  Yamaguchi Y  Nishida I  Akiyama K  Zakaria MP  Takada H 《Marine pollution bulletin》2002,45(1-12):325-331

Alkylbenzenes, molecular markers of sewage, were measured in 34 green mussels collected from India, Indonesia, Malaysia, Thailand, Cambodia, Vietnam, and the Philippines together with blue mussels collected from Tokyo Bay, Japan. Linear alkylbenzene (LAB) concentrations in South and South East Asian countries ranged from 10 to 1640 ng-∑LAB/g-dry tissue. In some populous cities, LAB concentrations were similar or higher than those found in northern Tokyo Bay which is heavily impacted by sewage effluents. I/E ratios (a ratio of internal to external isomers of LABs) in the South and South East Asian countries (1–3) were much lower than those in Tokyo Bay (3–8), indicating sewage discharged in the coastal zone is poorly treated (e.g., raw sewage and/or primary effluents). Alkylbenzenes with branched alkyl chains, tetrapropylene-based alkylbenzenes, were also detected in mussels from Indonesia and Philippines. This “tell-tale” sign indicates that poorly degradable detergents are still in use in this area, although they have long been phased-out in many industrialized countries.  相似文献   

Crustal structure of the Mizuho Plateau, East Antarctica from geophysical data     

Kiyoshi Ito  Akira Ikami 《Journal of Geodynamics》1986,6(1-4)

Various kinds of geophysical surveys have been carried out in the Mizuho Plateau, East Antarctica by the Japanese Antarctic Research Expeditions (JARE). The correlation between the high-level gravity anomaly and the bedrock elevation is examined along a route where both data are sufficient to permit deriving a crustal model from gravity, radio-echo sounding and explosion seismic data. The bedrock elevation usually correlates well with the high-level gravity anomaly. However, along the traverse route S-H-Z from the Syowa to Mizuho stations, the bedrock elevation has a weak negative correlation with the high-level gravity anomaly. Such a weak negative correlation is attributed to the deeper part of the crust.The crustal structure between the Syowa and Mizuho stations is modeled from the gravimetric data and the radio-echo sounding of bedrock elevations, so as to fit the P-wave velocity structure derived from the data of explosion seismic experiments. Then the structure is extended from Syowa Station seaward across Lützow-Holm Bay and from Mizuho Station southeastwards inland, where only gravimetric data are available. Thus, a crustal section about 600 km long is obtained on a margin of East Antarctica. The depth of the Moho increases by about 7 km from Syowa Station to the point Y200 (71° 46′S, 48° 56′E), about 500 km from the coast. A graben-like structure is obtained along the line across Lützow-Holm Bay. This suggests that both sides of the bay are bounded by faults.  相似文献   

The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western pacific ocean     

Ito  T.  Okita  T.  Ikegami  M.  Kanazawa  I. 《Journal of Atmospheric Chemistry》1986,4(4):401-411

In order to obtain a better understanding of the behavior of aerosols and SO₂ in the longrange transport through a marine boundary layer, a simple box-model is applied to the evaluation of the residence times of the species from the concentrations of gases and aerosols measured simulataneously on two islands in the West Pacific Ocean in the north-west monsoon. For Aitken and large particles, the residence time is varied from 3.7 to 7.4 days depending on the particle size, and their flux to the sea is equal to or slightly smaller than that of the free atmosphere. The residence time of giant particles is about one day and their flux to the sea is three times larger than that of the free atmosphere. The residence time of SO₂ is 15 hr, and the relative SO₂ mass flows of the deposition to the sea, of the diffusion to the free atmosphere and of the transformation to SO₄ ^2- are approximately 4, 1 and 1, respectively.  相似文献   

Tectonic evolution along the northernmost border of the Philippine Sea plate since about 1 Ma     

Tanio Ito  Kenichi Kano  Yo Uesugi  Kazuo Kosaka  Tatsuro Chiba 《Tectonophysics》1989,160(1-4):305-326

Recent structural, tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the Philippine Sea (PHS) plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the PHS plate and the Northeast Japan (NEJ) plate or the North American (NAM) plate since about 1 Ma. The authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage. A plate tectonic interpretation is proposed, based upon the tectonic evolution, with special reference to the mode of convergent motion. In brief, our interpretations are as follows: the relative motion between the PHS and the NEJ plates was not recognized geologically within the area studied from about 1.0 to 0.9 Ma (Stage 1), suggesting either none or small influence from the coupling between the two plates during that period of time. Convergence between the PHS and the NEJ plates was possibly in N-S direction from 0.9 to 0.5 Ma (Stage II), and probably north-northwestward since 0.5 Ma (Stages III to V). The mode of the convergent motion was that of buoyant subduction in Stages II and III. The mode changed gradually from buoyant subduction during Stage IV to collision in Stage V (0.07 Ma to the present).  相似文献   

Geophysical studies of crustal structure of the Ongul Islands and the Northern Mizuho Plateau, East Antarctica     

Akira Ikami  Kiyoshi Ito  Kazuo Shibuya  Katsutada Kaminuma 《Tectonophysics》1985,114(1-4)

Explosion seismic experiments, gravity measurements and aeromagnetic surveys were made in the northern Mizuho Plateau including the Ongul Islands, East Antarctica, from 1979 to 1982 by the Japanese Antarctic Research Expeditions. The objective of these field operations was to determine the crustal structure along the 300 km-long oversnow traverse route between Syowa and Mizuho Stations. Three big shots were fired; at sea near Syowa Station, in an ice hole near Mizuho Station and in an ice hole between both stations. Twenty-seven temporal seismic stations were set up along the route. Gravity measurements were carried out at 30 points along this route. Aeromagnetic surveys over the area were made four times.In the seismic experiments, clear refracted waves from the Conrad (estimated depth 30 km) and the Moho (estimated depth 40 km) discontinuities were recorded. No layer with a velocity of less than 6 km/s was found in the Ongul Islands nor beneath the ice sheet in the surveyed area. The P-wave velocity in the upper layer varies with depth from 6.0 km/s on the surface to 6.4 km/s at a depth of 13 km. Comparing the observed record section with synthetic seismograms, it was derived that the Conrad was not associated with a sharp velocity discontinuity, but a linear velocity increase of 0.55 km/s in a transition zone of 2.4 km thick. Velocities of P^* and P_n were determined as 6.95 km/s and 7.93 km/s assuming a flat layered structure.Bouguer gravity anomalies could not be calculated along the whole profile because of a lack of data on bedrock topography, so reduced gravity anomalies were calculated. These anomalies indicate no abrupt changes of the bedrock topography.  相似文献   

Paleoposition of Southwest Japan at 16 Ma: Implication from paleomagnetism of the Miocene Ichishi Group     

Akira Hayashida  Yoshihiko Ito 《Earth and Planetary Science Letters》1984,68(2):335-342

New paleomagnetic data from shallow-marine sediments of the Ichishi Group suggest a clockwise tectonic rotation of Southwest Japan in the Middle Miocene. Samples have been collected from mud or tuff layers at 17 sites. Stability of remanent magnetization has been examined by using alternating field and thermal demagnetization. The polarity sequence, composed of four normal and seven reversed polarity sites, is correlated to Polarity Epoch 16 (15.2–17.6 Ma), based on micropaleontological assignment of the upper Ichishi Group to Blow's Zone N8. The mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast. This result suggests that Southwest Japan was subjected to a clockwise rotation through 45° since 16 Ma. The clockwise rotation can be explained by the drift of Southwest Japan associated with the spreading of the Japan Sea during the Middle Miocene.  相似文献   

Role of Stress-controlled Flow Pathways in HDR Geothermal Reservoirs     

T. Ito  K. Hayashi 《Pure and Applied Geophysics》2003,160(5-6):1103-1124

— We addressed effects of in situ stress on the formation of flow pathways in fractured rocks in geothermal reservoirs, especially for HDR projects. Here we focused on fractures which are critically-stressed, causing shear slip in a current stress field. The sliding is likely to break sealing in the fractures and, as a result, to increase their permeability. Such a mechanism is possibly significant under high-temperature conditions at geothermal fields because of temperature enhancement on chemical reactions for the sealing. We present a procedure to estimate the orientation of the critically-stressed fractures relative to axes of in situ principal stress with the aid of the Mohr diagram. The procedure allows us to evaluate intuitively how the orientation changes with factors such as magnitude of in situ principal stresses and pore pressure. We applied the procedure to estimate possible orientations of the critically-stressed fractures in major HDR test sites. Results show that overall alignments of microseismicity during hydraulic stimulation are within predicted ranges for possible orientations of the critically-stressed fractures. Furthermore, it was found that if the state of in situ stress is not favorable to cause sliding of natural fractures, it tends to lead a high wellhead pressure at hydraulic stimulation and a high recovery rate at circulation. On the other hand, if the state of in situ stress is favorable for sliding, it tends vice versa to lead a low wellhead pressure at hydraulic stimulation and a low recovery rate at circulation.  相似文献   

Insights into operation of the subduction factory from the oxygen isotopic values of the southern Izu–Bonin–Mariana Arc     

Emi Ito  Robert J. Stern  Chuck Douthitt † 《Island Arc》2003,12(4):383-397

Abstract Oxygen is the most abundant element in the earth, and isotopic analysis of this element in island arc lavas potentially provides sensitive constraints on the proportion of oxygen recycled from subducted material, relative to that extracted from the mantle. Here we report on 225 new oxygen isotopic analyses of whole‐rock and glass samples, and clinopyroxene separates, from lavas collected from the southernmost 1500 km of the Izu–Bonin–Mariana (IBM) convergent margin. Whole‐rock samples clustered around a mean of 6.11 ± 0.47‰, whereas Mariana Trough glasses and mafic melts, calculated to be in equilibrium with mafic phenocrysts, clustered narrowly around a mean of 5.7‰. These data demonstrate that unequivocal identification of magmatic oxygen requires analysis of fresh glass or mafic minerals, and that the source of southern IBM Arc melts is entirely, or almost entirely, in equilibrium with normal mantle oxygen. If the elemental enrichments characteristic of the subduction component originate in subducted materials, these oxygen isotopic data are most consistent with the interaction of a small amount of sediment melt (<4%; mostly less than 1%) with mantle peridotite to yield the hybrid mantle that melts to form IBM Arc magmas.  相似文献   

新疆北部富蕴县沙尔布拉克玻安岩的地球化学特征及构造意义   总被引：19，自引：1，他引：19  

张海祥  牛贺才  于学元  Hiroaki Sato  Junichi Ito  单强 《地球化学》2003,32(2):155-160

详细的地球化学研究表明，新疆北部富蕴县沙尔布拉克中泥盆统北塔山组的辉石安山岩具有中等的SiO2含量（52.13%-60.45%)；高MgO(3.91%-9.31%)和相容元素（包括Ni、Cr、Co等）含量，以及高Mg^#和Al2O3／TiO2比值；低TiO2含量（0.21%-0.35%)；同时具有U型稀土元素分布模式；并强烈亏损高场强元素。这些特征均与玻安岩的地球化学特征一致，应属于玻安岩，形成于前弧环境。沙尔布拉克玻安岩的存在表明，古亚洲洋在早－中泥盆世向南发生了洋壳俯冲作用。  相似文献