NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic‐bearing fluids on Mars     

Yangting Lin  Ahmed El Goresy  Sen Hu  Jianchao Zhang  Philippe Gillet  Yuchen Xu  Jialong Hao  Masaaki Miyahara  Ziyuan Ouyang  Eiji Ohtani  Lin Xu  Wei Yang  Lu Feng  Xuchao Zhao  Jing Yang  Shin Ozawa 《Meteoritics & planetary science》2014,49(12):2201-2218

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ¹³C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO₂ and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.  相似文献   

A tribute to Ei Horikoshi (1932–2009)     

Masaaki Shimizu  Shigeru Otoh  Nigel J. Cook 《Resource Geology》2012,62(4):327-328

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Electron-positron pairs in a mildly relativistic plasma in active galactic nuclei     

Fumio Takahara  Masaaki Kusunose 《Astrophysics and Space Science》1986,119(1):217-219

We investigate the electron-positron pair concentration in an optically thin mildly relativistic plasma which is supposed to exist in active galactic nuclei. Firstly the equilibrium concentration is calculated when copious soft photons are supplied through the cyclotron higher harmonics. It is shown that the attainable states of the plasma are strongly restricted. Secondly we examine the pair production in a hot accretion plasma around a massive black hole, comparing relevant time scales. We find that significant pair production occurs when the accretion rate is moderately high and the infall velocity is slow compared to the free fall.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984  相似文献   

Silver in Tokyo Bay estuarine waters and Japanese rivers     

Yan Zhang  Hajime Obata  Toshitaka Gamo 《Journal of Oceanography》2008,64(2):259-265

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg⁻¹, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg⁻¹). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log K_d > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y⁻¹ and 15 kg y⁻¹, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.  相似文献   

Long-term bottom water warming in the north Ross Sea     

Hirokazu Ozaki  Hajime Obata  Mikio Naganobu  Toshitaka Gamo 《Journal of Oceanography》2009,65(2):235-244

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.  相似文献   

南海大气季节内振荡特征及其与ENSO循环的关系   总被引：3，自引：2，他引：1       下载免费PDF全文

祝丽娟  王亚非  高桥正明 《大气科学学报》2014,37(1):9-18

采用1979—2009年NCEP/NCAR再分析资料、NOAA向外长波辐射(outgoing long-wave radiation,简称OLR)及扩展重建海表面温度资料,对南海大气季节内振荡(Intra-seasonal Oscillation,简称ISO)特征及其与ENSO循环的关系进行了诊断分析。结果表明:1)南海大气ISO的30~60 d周期在5—10月均显著。一般年南海大气ISO的对流传播在纬向上存在东传和西传,在经向上具有南北半球季节性摆动的特征。以低频动能表征的南海大气ISO强度年代际变化特征明显,近31 a来趋势增强,年变化呈单峰结构,峰值在7—8月。2)南海大气ISO的对流与ENSO循环显著相关,其强度在El Nio(La Nia)年减弱(增强)。与一般年对比,南海大气ISO对流在El Nio和La Nia年均表现为西传减弱、北传显著。北传特征表现为强对流活跃带于春季(4—5月)北跳至北半球(在La Nia年最北可至35°N),但在北半球的传播方向与一般年相比存在显著差异。3)南海大气ISO强度与ENSO循环关系密切,在El Nio(La Nia)年减弱(增强),两者表现为约半年(6~8个月)的滞后相关。Nio3区海表面温度异常序列与南海大气ISO强度的相关在中西太平洋地区和El Nio成熟前的春、秋季最显著,同时相关中心伴随低频动能高值区东移。  相似文献   

Magnetic Reconnection, Turbulence, and Collisionless Shock     

Hantao Ji  Russell Kulsrud  Masaaki Yamada 《Astrophysics and Space Science》2005,298(1-2):219-226

A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection. The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas. Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common in energetic astrophysical phenomena.  相似文献   

On the opaque core appearing in the early phase of star formation     

Masaaki Kondo 《Earth, Moon, and Planets》1978,19(2):245-252

The spherical collapse of a protostar with one solar mass is calculated from a gravitationally unstable initial stage, by solving the equations of hydrodynamics and pherical radiative transfer. The temperature dependence of the dust opacity is taken into account in contrast to the earlier calculations with temperature independent opacities. It is shown that the opaque core is equivalent to the adiabatic core in the purely adiabatic case. The blanketing effect of dust grains strengthens the shock of the opaque core and may result in raising the central entropy of protostars.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.  相似文献   

Stratigraphy and optically stimulated luminescence (OSL) dating of a Quaternary sequence along the Dong Nai River, southern Vietnam   总被引：1，自引：0，他引：1  

Toshiyuki Kitazawa  Takahiro Nakagawa  Tetsuo Hashimoto  Masaaki Tateishi 《Journal of Asian Earth Sciences》2006,27(6):788-804

The pre-Holocene Cenozoic sequence outcrops in the terrestrial part of the eastern margin of the Mekong Basin. However, the stratigraphy of the sequence is still unclear. Its detailed stratigraphy and chronology were therefore studied along the Dong Nai River, southern Vietnam, and the lithofacies and the relations among the formations were investigated from the outcrops. The ages of the deposits were determined by using optically stimulated luminescence (OSL) dating.The Ba Mieu Formation was deposited about 176±52 ka during marine isotope stage (MIS) 7–6. The Thu Duc Formation was deposited about 97±27 ka during MIS 5. Both the Ba Mieu and Thu Duc formations are composed of fluvial and tidally influenced coastal deposits. The newly proposed Nhon Trach Formation was originally an eolian (blanket) deposit, but it has been partly reworked by fluvial processes. The Nhon Trach Formation was deposited about 10.9±4.7 ka, in the last part of the Pleistocene to the beginning of the Holocene. The OSL ages for the Ba Mieu, Thu Duc, and Nhon Trach formations are younger than the ages previously assigned to these formations.  相似文献   

Origin of eclogite and garnet pyroxenite from the Moldanubian Zone of the Bohemian Massif, Czech Republic and its implication to other mafic layers embedded in orogenic peridotites     

M. Obata  T. Hirajima  M. Svojtka 《Mineralogy and Petrology》2006,88(1-2):321-340

Summary The granulite terrane of the Czech part of the Gf?hl unit includes numerous small bodies of mantle derived peridotite, some of which contain layers or lenses of eclogite and garnet pyroxenite. These eclogitic rocks have generally been considered to be high-pressure crystal cumulates formed in the upper mantle. We present new analyses of whole-rock major and trace element contents for three kynanite-quartz eclogite samples taken from the Nové Dvory garnet peridotite body. Integrating these data with previously published analyses from the literature on eclogitic rocks from this terrane, we demonstrate that a magnesian group of eclogites, including these three new samples, were originally formed as cumulus gabbros, which were later transformed to eclogites in the mantle. A gabbroic origin for some mafic layers (Type II) has been advocated for other orogenic peridotites, such as Beni Bousera (Morocco), Ronda (Spain), and Horoman (Japan). By comparing these sets of data with those from the Bohemian Massif, we propose a simple method of identifying groups of metagabbros by utilizing MgO-normalization in oxide ratio plots for whole-rock major element analyses.  相似文献