A 27-kyr record of environmental change in central Asia inferred from the sediment record of Lake Hovsgol,northwest Mongolia   总被引：1，自引：0，他引：1  

Takuma Murakami  Nagayoshi Katsuta  Koshi Yamamoto  Nobuki Takamatsu  Masao Takano  Takefumi Oda  Genki I. Matsumoto  Kazuho Horiuchi  Takayoshi Kawai 《Journal of Paleolimnology》2010,43(2):369-383

Geochemistry of a sediment core from Lake Hovsgol, northwest Mongolia provides a continuous, 27-kyr history of the response of the lake and the surrounding catchment to climate change. Principle component (PC) analysis of 19 major and trace elements, total inorganic carbon (TIC), and total organic carbon (TOC) in the bulk sediment samples revealed that the 21 chemical components can be grouped into four assemblages—group-1: Na, Mg, Ca, Sr, and TIC, hosted in carbonate minerals (calcite, dolomite, and magnesian calcite); group-2: Ni, Cu, and Zn, recognized as biophilic trace metals, and TOC; group-3: Al, K, Ti, V, Fe, Rb, Cs, Ba, and Pb, composed of rock-forming minerals; and group-4: Cr, Mn, and As, sensitive to the redox condition of the sediment. The four element assemblages originated from three relevant processes. Group-1 and group-2 components are authigenic products and comprise the end member on the PC-1 score, whose variation reflects changes in the water volume, i.e. the balance between precipitation and evaporation (P/E). Group-3 components from detrital materials of the catchment contribute to the PC-2 score, whose variability indicates erosion/weathering intensity in the drainage basin, which might be controlled by the amount of vegetation cover associated with moisture change. The group-4 components of redox-sensitive elements contribute to the PC-3 score and are not an end member because of their small amount. The first two PC scores suggest a sequential record of paleo-moisture evolution in central Asia. The P/E balance in the Lake Hovsgol region, inferred from the PC-1 score, gradually increased during the glacial/interglacial transition. This resembles climate change of the North Atlantic region on the glacial–interglacial scale, but does not reflect the abrupt climate shifts such as the warm Bølling-Allerød and the cold Younger Dryas of the North Atlantic on the millennial scale. A periodic variation of ~8.7 kyr was observed in the PC-2 score profile of detrital input to Lake Hovsgol over the last glacial and Holocene. The decrease in detrital input coincided with the copious supply of moisture from the Asian monsoon regime and the North Atlantic westerly winds to the Baikal drainage basin, which includes Lake Hovsgol. Our geochemical records from Lake Hovsgol demonstrate that the climate system of interior continental Asia was strongly influenced by change on both Milankovitch and sub-Milankovitch scales.  相似文献   

Elasticity of MgO to 130 GPa: Implications for lower mantle mineralogy     

Motohiko Murakami  Yasuo Ohishi  Naohisa Hirao  Kei Hirose 《Earth and Planetary Science Letters》2009,277(1-2):123-129

The aggregate shear wave velocities of MgO (periclase) have been determined throughout Earth's lower mantle pressure regime approaching 130 GPa using Brillouin spectroscopy in conjunction with synchrotron X-ray diffraction technique in a diamond anvil cell apparatus. We found that the extrapolations of the high-pressure shear wave velocities and shear moduli to ambient pressure are highly consistent with earlier studies. However, the measurements over a wide pressure range revealed that the pressure derivative of the shear modulus (dG/dP = G₀′) of MgO is 1.92(2), which is distinctly lower than that of previous lower-pressure experiments. Compared with the previous results on (Mg,Fe)O ferropericlase, there is no clear correlation between iron content and G₀′. We calculate that the shear wave velocity profile of lower mantle along the adiabatic geotherm applied by the lower G₀′ value of periclase can remarkably well reproduce the global seismological 1-D velocity profile model with uniform composition model. The best-fitting result indicates the possibility of a lower mantle mineralogy with ~ 92 vol.% silicate perovskite phase, implying that the bulk composition of lower mantle is likely not to be pyrolitic but more chondritic. The present acoustic measurements performed over the large pressure range have thus led us to a better understanding of compositional model of the Earth's lower mantle.  相似文献   

Does heavy oil pollution induce bacterial diseases in Japanese flounder Paralichthys olivaceus?   总被引：1，自引：1，他引：0  

Jun-Young Song  Kei Nakayama  Yasunori Murakami  Sung-Ju Jung  Myung-Joo Oh  Satoru Matsuoka  Hidemasa Kawakami  Shin-Ichi Kitamura   《Marine pollution bulletin》2008,57(6-12):889

As basic research for the effect of heavy oil on the fish immune system, in this study, the number of leukocyte was counted in Japanese flounder Paralichthys olivaceus, after exposure to heavy oil at a concentration of 30 g/8 L for 3 days. To compare the numbers of bacteria in the skin mucus between oil-exposed and control fish, viable bacteria were enumerated by counting colony forming unit (CFU). Compared with 5.79 ± 1.88 × 10⁷ leukocytes/mL in the controls, the exposed fish demonstrated higher counts, averaging 1.45 ± 0.45 × 10⁸ cells/mL. The bacterial numbers of control fish were 4.27 ± 3.68 × 10⁴ CFU/g, whereas they were 4.58 ± 1.63 × 10⁵ CFU/g in the exposed fish. The results suggest that immune suppression of the fish occurred due to heavy oil stressor, and bacteria could invade in the mucus, resulting in the increasing leukocyte number to prevent infectious disease.  相似文献   

Toxicogenomic analysis of immune system-related genes in Japanese flounder (Paralichthys olivaceus) exposed to heavy oil   总被引：1，自引：1，他引：0  

Kei Nakayama  Shin-Ichi Kitamura  Yasunori Murakami  Jun-Young Song  Sung-Ju Jung  Myung-Joo Oh  Hisato Iwata  Shinsuke Tanabe 《Marine pollution bulletin》2008,57(6-12):445

Heavy oil contamination is one of the most important environmental issues. Toxicities of polycyclic aromatic hydrocarbons (PAHs), including immune toxicities, are well characterized, however, the immune toxic effects of heavy oil, as a complex mixture of PAHs, have not been investigated. In the present study, we selected Japanese flounder (Paralichthys olivaceus) as a model organism, and observed alteration of immune function by the exposure to heavy oil. To analyze the expression profiles of immune system-related genes, we selected 309 cDNAs from our flounder EST library, and spotted them on a glass slide. Using this cDNA array, alteration of gene expression profiles was analyzed in the kidneys of flounders exposed to heavy oil. Six Japanese flounders (mean body weight: 197 g) were acclimated to laboratory conditions at 19–20 °C. Three fish were exposed to heavy oil C (bunker C) at a concentration of 3.8 g/L for 3 days, and the others were kept in seawater without heavy oil and used as the control. After the exposure period, the fish were transferred into control seawater and maintained for 4 days, and then they were dissected and their kidneys were removed. Total RNA was extracted from the kidney samples to use in gene expression analyses. The microarray detected alteration of immune system-related genes in the kidneys of heavy oil-exposed flounders, including down-regulation of immunoglobulin light chain, CD45, major histocompatibility complex class II antigens and macrophage colony-stimulating factor precursor, and up-regulation of interleukin-8 and lysozyme. These results suggest that pathogen resistance may be weakened in heavy oil-exposed fish, causing a subsequent bacterial infection, and then proinflammatory genes may be induced as a defensive response against the infection. Additionally, we found candidate genes for use as biomarkers of heavy oil exposure, such as N-myc downstream regulated gene 1 and heat shock cognate 71 kDa proteins.  相似文献   

Pyrene induces a reduction in midbrain size and abnormal swimming behavior in early-hatched pufferfish larvae     

Yuki Sugahara  Masahumi Kawaguchi  Tatsuya Itoyama  Daisuke Kurokawa  Yasuhiko Tosa  Shin-Ichi Kitamura  Itsuki C. Handoh  Kei Nakayama  Yasunori Murakami 《Marine pollution bulletin》2014

Spills of heavy oil (HO) have an adverse effect on marine life. We have demonstrated previously that exposure to HO by fertilized eggs of the pufferfish (Takifugu rubripes) induces neural disruption and behavioral abnormality in early-hatched larvae. Here, two kinds of polycyclic aromatic hydrocarbons, pyrene and phenanthrene, were selected to examine their toxic effects on larval behavior of another pufferfish species (T. niphobles). Larvae exposed to pyrene or phenanthrene exhibited no abnormalities in morphology. However, those exposed to pyrene but not phenanthrene swam in an uncoordinated manner, although their swimming distance and speed were normal. The optic tectum, a part of the midbrain, of pyrene-exposed larvae did not grow to full size. Thus, these findings are indicated that pyrene might be a contributor to the behavioral and neuro-developmental toxicity, although there is no indication that it is the only compound participating in the toxicity of the heavy oil mixture.  相似文献   

Preface     

Kohtaro Hosoda  Hiroshi Murakami  Akira Shibata  Futoki Sakaida  Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):291-291

ADEOS-II Ocean: Advanced Earth Observing Satellite-II Ocean

Preface  相似文献   

A new index for evaluation of risk of complex disaster due to typhoons     

Tomokazu Murakami  Shinya Shimokawa  Jun Yoshino  Takashi Yasuda 《Natural Hazards》2015,79(1):29-44

  相似文献   

Resolution dependence of tropical cyclone formation in CMIP3 and finer resolution models   总被引：1，自引：0，他引：1  

Kevin Walsh  Sally Lavender  Enrico Scoccimarro  Hiroyuki Murakami 《Climate Dynamics》2013,40(3-4):585-599

Detection of tropical lows is performed in a suite of climate model simulations using objectively-determined detection thresholds that are resolution-dependent. It is found that there is some relationship between model resolution and tropical cyclone formation rate even after the resolution-dependent tropical cyclone detection threshold is applied. The relationship is investigated between model-simulated tropical cyclone formation and a climate-based tropical cyclone Genesis Potential Index (GPI). It is found that coarser-resolution models simulate the GPI better than they simulate formation of tropical cyclones directly. As a result, there appears to be little relationship from model to model between model GPI and the directly-simulated cyclone formation rate. Statistical analysis of the results shows that the main advantage of increasing model resolution is to give a considerably better pattern of cyclone formation. Finer resolution models also simulate a slightly better pattern of GPI, and for these models there is some relationship between the pattern of GPI simulated by each model and that model’s pattern of simulated tropical cyclone formation.  相似文献   

Will the South Asian monsoon overturning circulation stabilize any further?     

R. Krishnan  T. P. Sabin  D. C. Ayantika  A. Kitoh  M. Sugi  H. Murakami  A. G. Turner  J. M. Slingo  K. Rajendran 《Climate Dynamics》2013,40(1-2):187-211

Understanding the response of the South Asian monsoon (SAM) system to global climate change is an interesting scientific problem that has enormous implications from the societal viewpoint. While the CMIP3 projections of future changes in monsoon precipitation used in the IPCC AR4 show major uncertainties, there is a growing recognition that the rapid increase of moisture in a warming climate can potentially enhance the stability of the large-scale tropical circulations. In this work, the authors have examined the stability of the SAM circulation based on diagnostic analysis of climate datasets over the past half century; and addressed the issue of likely future changes in the SAM in response to global warming using simulations from an ultra-high resolution (20 km) global climate model. Additional sensitivity experiments using a simplified atmospheric model have been presented to supplement the overall findings. The results here suggest that the intensity of the boreal summer monsoon overturning circulation and the associated southwesterly monsoon flow have significantly weakened during the past 50-years. The weakening trend of the monsoon circulation is further corroborated by a significant decrease in the frequency of moderate-to-heavy monsoon rainfall days and upward vertical velocities particularly over the narrow mountain ranges of the Western Ghats. Based on simulations from the 20-km ultra high-resolution model, it is argued that a stabilization (weakening) of the summer monsoon Hadley-type circulation in response to global warming can potentially lead to a weakened large-scale monsoon flow thereby resulting in weaker vertical velocities and reduced orographic precipitation over the narrow Western Ghat mountains by the end of the twenty-first century. Supplementary experiments using a simplified atmospheric model indicate a high sensitivity of the large-scale monsoon circulation to atmospheric stability in comparison with the effects of condensational heating.  相似文献   

Quantification of atmospheric oxygen levels during the Paleoproterozoic using paleosol compositions and iron oxidation kinetics     

Takashi Murakami  Bulusu Sreenivas  Subrata Das Sharma 《Geochimica et cosmochimica acta》2011,75(14):3982-4004

The increase in atmospheric oxygen during the Precambrian is a key to understand the co-evolution of life and environment and has remained as a debatable topic. Among various proxies for the estimation of atmospheric oxygen levels, paleosols, ancient weathering profiles, can provide a quantitative pattern of atmospheric oxygen increase during the Precambrian period of Earth history. We have re-evaluated the chemical compositions of paleosols, and presented a new method of applying Fe²⁺ oxidation kinetics to the Fe²⁺ and Fe³⁺ concentrations in paleosols to decipher the quantitative partial pressure of atmospheric oxygen (P_O2) between 2.5 and 2.0 Ga. We first estimated the compaction factor (CF, the fraction of original thickness) using the immobile elements such as Ti, Al and Zr on equal volume basis, which was then used to calculate retention fractions (M_R), a mass ratio of paleosol to parent rock, of redox-sensitive elements. The CF and Fe_R values were evaluated for factors such as homogeneity of immobile elements, erosion, and formation time of weathering. Fe_R increased gradually within the time window of ∼2.5-2.1 Ga and remained close to 1.0 since ∼2.1 Ga onwards. Mn_R also increased gradually similar to Fe_R but at a slower rate and near complete retention was observed ∼1.85 Ga, suggesting an almost continuous increase in the oxidation of Fe²⁺ and Mn²⁺ in paleosols ranging in age between ∼2.5 and 1.9 Ga.We have modeled P_O2 variations during the Paleoproterozoic by applying Fe²⁺ oxidation kinetics to the Fe²⁺ and Fe³⁺ concentrations in paleosols, which enabled us to derive an Fe²⁺ oxidation term referred to as ψ. Possible changes in temperature and P_CO2 during this time window and their effects on resulting models of P_O2 evolution have been also considered. We assumed four cases for the calculations of P_O2 variations between 2.5 and 2.0 Ga: no change in either temperature or P_CO2, long-term change in only P_CO2, long-term changes in both temperature and P_CO2, and short-term fluctuations of both temperature and P_CO2 during the possible, multiple global-scale glaciations. The calculations indicate that P_O2 increased gradually, linearly on the logarithmic scale, from <∼10⁻⁶ to >∼10⁻³ atm between 2.5 and 2.0 Ga. Our calculations show that the P_O2 levels would have fluctuated significantly, if intense, global glaciation(s) followed by period(s) of high temperature occurred during the Paleoproterozoic. This gradual rise model proposes a distinct, quantitative pattern for the first atmospheric oxygen rise with important implications for the evolution of life.  相似文献