Observation of oceanic structure around Tosa-Bae southeast of Shikoku     

Yoshihiko Sekine  Haruki Ohwaki  Motoya Nakagawa 《Journal of Oceanography》1994,50(5):543-558

The hydrographic observations in the vicinity of a seamount, the Tosa-Bae, southeast of Shikoku have been carried out two times in summer of 1991 and 1992. The temperature, salinity fields are observed by CTD and velocity fields are measured by ADCP. Results of these observation are presented in this paper. It is shown that salinity maximum water at a depth of 100 m is confined to a southeastern are of the Tosa-Bae, however, salinity minimum water is found in northern side of the Tosa-Bae. This indicates the westward intrusion of less saline water over northern slope. A positive correlation is detected between the estimated Rossby height (fL/N) and the observed height of Taylor Column estimated from the vertical change in the isotherms and isohalines. Almost both heights give smaller value than representative depth of bottom topography of the Tosa-Bae, it is indicated that the topographic effect of the Tosa-Bae is not fully reached to the surface. From the correlations between the vertical difference of geostrophic flow and that of ADCP velocity, ageostrophic flow component is detected.  相似文献   

Effects of soft x-ray flux on the lower solar atmosphere in flares     

J. C. Henoux  Y. Nakagawa 《Solar physics》1977,53(1):279-280

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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   

两个相连湖泊的微生态系统——云南高原湖泊中浅水的星云湖和深水的抚仙湖研究   总被引：4，自引：0，他引：4  

大久保贤治  熊谷道夫  坂本充  宋学良  张子雄 《云南地理环境研究》2002,14(2):10-19

抚仙湖是中国云南省的一个深水湖，连接着富营养化的浅水湖－－星云湖，星云湖排放含绿藻的水进入抚仙湖。两湖位于省会昆明附近，由于地方文化、集约化农业、以及旅游业的发展，两湖已经富营养化。因为湖泊体积容量的级别差异，深水湖的富营养化几乎没被注意，抚仙湖秋季下层滞水带缺氧已经关注了20年，似乎下层滞水带是深水湖富营养化的指标或趋势。抚仙湖看起来目前情况尚好，可以说寡营养，然而，外界负荷是潜在的，且是以稳定的加速度进行的。在此对浅水湖富营养化的原因进行了讨论，包括在其它云南湖泊观察到富营养化的过程，再者，对两个连相湖的藻和蓝藻碎片的大小构成进行比照。为了与深水的抚仙湖状况进行比较，简略介绍了一个日本的深湖及其径流系统。其中，涡流和它的微生态系统，在两者中相关性很好。对于以涡流生态系统的见解判断微生态系统的深水湖富营养化问题将给予概括。  相似文献   

Transformation of arsenic compounds in modern intertidal sediments of Iriomote Island, Japan   总被引：1，自引：0，他引：1  

Harue Masuda  Yoshito Yamatani  Mitsuru Okai   《Journal of Geochemical Exploration》2005,87(2):587-81

The arsenic accumulation process in intertidal sediments of Iriomote Island, Japan, is analyzed as a naturally balanced arsenic-fixation system. Major and minor element chemistry is analyzed by X-ray fluorescence photometry, mineralogy is investigated by X-ray diffractometry, and four arsenic compounds are characterized by hydrogen-generated atomic absorption photometry. It is found that arsenic is accumulated by iron hydroxides/oxides precipitated following the decomposition of humic acids in the shallower sediment, and is subsequently incorporated into iron sulfide minerals at depth. The arsenic is immobile during incorporation into arsenic-bearing phases, suggesting that arsenic is unlikely to be released into the porewater under natural conditions in early diagenesis. The formation and decomposition of arsenic-bearing organic compounds appear to be associated with the formation and decomposition of arsenic in oxyhydroxides/oxides, suggesting that microbial activity may play an important role in controlling the behavior of arsenic and arsenic-bearing phases in the sediment column.  相似文献   

Changes in fish community in seagrass beds in Mangoku-ura Bay from 2009 to 2014, the period before and after the tsunami following the 2011 off the Pacific coast of Tohoku earthquake     

Jun Shoji  Mitsuru Morimoto 《Journal of Oceanography》2016,72(1):91-98

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The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献   

Are C1 chondrites chemically fractionated? a trace element study     

Mitsuru Ebihara  Rainer Wolf  Edward Anders 《Geochimica et cosmochimica acta》1982,46(10):1849-1861

Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for the elements Ag, Au, Bi, Br, Cd, Ce, Cs, Eu, Ge, In, Ir, Lu, Nd, Ni, Os, Pd, Pt, Rb, Re, Sb, Se, Sn, Tb, Te, Tl, Yb, and Zn. The data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in C1 chondrites.A number of elements (Br, Rb, Cs, Au, Re, Os, Ni, Pd, Sb, Bi, In, Te) show small but correlated variations. Those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body, whereas those of Sb, Bi, In, and Te may at least in part involve nebular processes. Br and Au show systematic abundance differences from meteorite to meteorite, which suggests hydrothermal transport on a kilometer scale. The remaining elements vary from sample to sample, suggesting transport on a centimeter scale.There is no conclusive evidence for nebular fractionation affecting C1 's. Though C1 chondrites have lower $\text{Zr}\text{Hf}$ and $\text{Ir}\text{Re}$ ratios than do other chondrite classes, these ratios vary in other classes, suggesting that those classes rather than C1's are fractionated. Three fractionation-prone REE—Ce, Eu, and Yb have essentially the same relative abundances in C1's and all other chondrite classes, and hence apparently are not fractionated in C1's. We did not confirm the large Tb and Yb variations in C1's reported by other workers.We present revised mean C1 abundances for 35 elements, based on the new data and a critical selection of literature data. Changes are generally less than 10%, except for Br, Rb, Ag, Sb, Te, Au, and the REE.The Plainview C2 xenolith has normal trace element abundances, except for 3 elements falling appreciably above the C2 range: Rb, Cs, and Bi. Hydrothermal alteration may be the reason for all 3, though nebular fractionation remains a possibility for Bi.  相似文献   

Material flows of an evolving magnetic field     

Yoshinari Nakagawa 《Astrophysics and Space Science》1990,174(1):95-109

The possibility of material flows to trace out the magnetic field configuration is examined through numerical simulations. In particular, the evolution of a magnetic arcade due to differential motions of its footpoints is considered. With the use of numerical scheme based on the method of projected characteristics and newly derived proper boundary conditions, it is shown that material flows develop to outline the configuration of evolving magnetic field. Physical implications of the results are discussed.  相似文献   

Dissolution of silica accompanied by oxygen consumption in the bottom layer of Japan’s central Seto Inland Sea in summer     

Kazuo Abe  Norihisa Nakagawa  Katsuyuki Abo  Mutsumi Tsujino 《Journal of Oceanography》2014,70(3):267-276

Distribution of silicic acid (Si(OH)₄) in bottom water was investigated in the central Seto Inland Sea under stratified conditions in summer. Water samples were collected at 10 stations on April 24 and 25 and July 7 and 8, 2012. In July, stratification progressed, and a cold water mass (dome) of <20 °C appeared. In response to the cold dome, low oxygen content was observed in the bottom layer of the eastern part of Hiuchi-Nada. In this water mass site, apparent oxygen utilization values calculated from dissolved oxygen (DO) concentrations increased, coinciding with increase of Si(OH)₄ concentrations from April to July. This suggests that increase of Si(OH)₄ [dissolution of biogenic silica (diatom frustules)] was accompanied by DO consumption due to degradation of organic matter such as plankton soft tissue. These findings suggest that a bacterial degradation of the organic matrix that covers diatom frustules could accelerate the dissolution of biogenic silica in bottom water under stratified conditions.  相似文献