Polyunsaturated fatty acids in a lacustrine sediment as a possible indicator of paleoclimate     

Kimitaka Kawamura  Ryoshi Ishiwatari 《Geochimica et cosmochimica acta》1981,45(2):149-155

Polyunsaturated fatty acids (C_18:2 and C_18:3ω3 were analyzed in the upper 20m layer of a 200 m long sediment core taken from Lake Biwa. Concentration maxima occur in layers at depths of 0.2, 1–5, 11–12, and 16m. The vertical changes in the $\text{(C}{}_{\mathrm{18:2}}\text{C(C}{}_{\mathrm{18:0}}$ ratio appear to correlate with paleoclimatic condition suggested from palynological evidence. On the basis of $\text{C}{}_{\mathrm{18:2}}\text{C}{}_{\mathrm{18:0}}$ ratios, it was suggested that it has been colder at 200, 1000–4000, 15,000 and 20,000 yr BP than at other times.  相似文献   

Fine structure of laboratory wind-wave surfaces studied using an optical method     

Naoto Ebuchi  Hiroshi Kawamura  Yoshiaki Toba 《Boundary-Layer Meteorology》1987,39(1-2):133-151

The fine structure of laboratory wind-wave surfaces was investigated using an optical method. Several characteristic structures, closely associated with wind speed and the stage of development of the waves, are described. A parallel light, incident on the wind-wave surface, was backscattered by specular facets perpendicular to the incident angle. These specular facets, which represented the fine structures, were photographed and quantitatively analyzed by image processing techniques.For wind speeds ranging from 3.6 to 13.6 m s^–1, different types of small-scale undulations appeared: a three-dimensional rhombic structure; a train of capillary waves on the forward face with wavelengths gradually decreasing with distance from the crest, and a streaky structure on the backward face in the direction of the wind; and random and wide-spreading irregularities covering the whole wind-wave surface. The spatial scales and temporal variation of the undulations are described.  相似文献   

Fatty acid geochemistry of a 200 m sediment core from Lake Biwa,Japan. Early diagenesis and paleoenvironmental information     

Kimitaka Kawamura  Ryoshi Ishiwatari 《Geochimica et cosmochimica acta》1984,48(2):251-266

Fatty acids (FAs), β- and ω-hydroxy acids, α,ω-dicarboxylic acids and n-alkanes were studied in a 200 m sediment core taken from Lake Biwa, Japan. FAs showed bimodal distribution with peaks at C₁₆ and C₂₂-C₂₈. Their distribution patterns clearly changed with depth from lower molecular weight (C₁₂-C₁₉) predominance to higher molecular weight (C₂₀-C₃₂) predominance in the upper 20 m interval. Analyses of related compounds (β- and ω-hydroxy acids and α, ω-dicarboxylic acids) suggest that β- and ω-oxidative degradation of C₁₂-C₁₉ FAs has occurred in the sediments.The ratio of bound C₁₂-C₁₉ to unbound FAs increases with depth in the upper 0–1 m sediments, suggesting that unbound FAs are more labile. However, the ratio varies significantly in deeper sections and may be associated with water temperature.In the sediments deeper than 20 m in depth, C₁₂-C₁₉ FAs gradually decrease. On the other hand, higher molecular weight FAs (HFAs: C₂₀-C₃₂), which were probably derived from terrestrial plants, increase in concentration from 20 m to 100 m, suddenly decrease at 100 m and show progressively lower concentration in deeper sediments. These fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin. ω-Hydroxy C₂₀-C₃₀ acids and C₂₀-C₃₀α, ω-dicarboxylic acids show a distribution pattern similar to HFAs. Branched chain FAs, ω-hydroxy acids and C₉-C₁₉α,ω-dicarboxylic acids show a major peak around 3–15 m in depth. This peak is probably caused by increased bacterial activity in the water column and surface sediments in the past, which may be associated with an increase in primary production of the lake.  相似文献   

A Review on the Currents in the South China Sea: Seasonal Circulation, South China Sea Warm Current and Kuroshio Intrusion   总被引：47，自引：4，他引：43  

Jianyu Hu  Hiroshi Kawamura  Huasheng Hong  Yiquan Qi 《Journal of Oceanography》2000,56(6):607-624

Researches on the currents in the South China Sea (SCS) and the interaction between the SCS and its adjacent seas are reviewed. Overall seasonal circulation in the SCS is cyclonic in winter and anticyclonic in summer with a few stable eddies. The seasonal circulation is mostly driven by monsoon winds, and is related to water exchange between the SCS and the East China Sea through the Taiwan Strait, and between the SCS and the Kuroshio through the Luzon Strait. Seasonal characteristics of the South China Sea Warm Current in the northern SCS and the Kuroshio intrusion to the SCS are summarized in terms of the interaction between the SCS and its adjacent seas.  相似文献   

A-HIGHERS—The System to Produce the High Spatial Resolution Sea Surface Temperature Maps of the Western North Pacific Using the AVHRR/NOAA   总被引：1，自引：0，他引：1  

Futoki Sakaida  Jun-ichi Kudoh  Hiroshi Kawamura 《Journal of Oceanography》2000,56(6):707-716

To study on the oceanic variations in the western North Pacific, we developed a system to produce a high spatial resolution sea surface temperature (SST) map from the data obtained by the Advanced Very High Resolution Radiometer (AVHRR) aboard the National Oceanic and Atmospheric Administration (NOAA) satellites. As the system has been improved on the HIGHERS (Sakaida and Kawamura, 1996), it is called the Advanced-HIGHERS (A-HIGHERS). The A-HIGHERS has been developed on the super computer in the Tohoku University, which is favorable for handling of a large volume of data. Mainly because of improvements in the cloud detection algorithm, the A-HIGHERS can deal with the data obtained at dawn and dusk around the year, and at daytime in summer more effectively. The A-HIGHERS are used to produce SST maps spanning from (60°N, 120°E) to (20°N, 160°E) with a grid size of 0.01 degree.  相似文献   

Climatology of hot events in the western equatorial Pacific     

Anindya Wirasatriya  Hiroshi Kawamura  Teruhisa Shimada  Kohtaro Hosoda 《Journal of Oceanography》2015,71(1):77-90

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Evidences of increasing primary production in the ocean by Stommel's perpetual salt fountain     

Shigenao Maruyama  Takashi YabukiTetsuya Sato  Koutaro TsubakiAtsuki Komiya  Mikihito WatanabeHiroshi Kawamura  Katsumi Tsukamoto 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):567-574

The American physical oceanographer Henry Stommel and co-workers proposed “the perpetual salt fountain” and suggested the possibility of upwelling deep seawater without an energy source. In the open ocean, deep seawater containing rich nutrients becomes a source of primary production. Previously, we have tested Stommel's hypothesis by numerical simulations and in ocean experiments, and confirmed the upwelling of a perpetual salt fountain. In the present study, we conducted an open-ocean experiment in the Philippines Sea, and succeeded to demonstrate an increase in chlorophyll concentration. The chlorophyll concentration at the pipe outlet was much greater than that in the surrounding seawater. Satellite ocean-color image around the pipe was analyzed, and the signal of artificial upwelling is investigated. Composite analysis of satellite chlorophyll image indicates an increased surface chlorophyll distribution in the vicinity of pipe position, in which the increasing signal is much larger than the expected production based on nutrient supply. Although the problem must be further discussed, this increased signal is shown to be statistically significant. This mechanism may contribute to effective utilization of fishery resources in subtropical oligotrophic region.  相似文献   

Sublimation’s impact on temporal change of albedo dichotomy on Iapetus     

Jun Kimura  Taichi Kawamura  Tomokatsu Morota  Kiyoshi Kuramoto  Tatsuaki Okada 《Icarus》2011,214(2):596-605

Iapetus, one of the saturnian moons, has an extreme albedo contrast between the leading and trailing hemispheres. The origin of this albedo dichotomy has led to several hypotheses, however it remains controversial. To clarify the origin of the dichotomy, the key approach is to investigate the detailed distribution of the dark material. Recent studies of impact craters and surface temperature from Cassini spacecraft data implied that sublimation of H₂O ice can occur on Iapetus’ surface. This ice sublimation can change the albedo distribution on the moon with time.In this study, we evaluate the effect of ice sublimation and simulate the temporal change of surface albedo. We assume the dark material and the bright ice on the surface to be uniformly mixed with a certain volume fraction, and the initial albedo distribution to incorporate the dark material deposits on the surface. That is, the albedo at the apex is lowest and concentrically increases in a sinusoidal pattern. This situation simulates that dark materials existed around the Iapetus’ orbit billions of years ago, and the synchronously rotating Iapetus swept the material and then deposited it on its surface. The evolution of the surface albedo during 4.0 Gyr is simulated by estimating the surface temperature from the insolation energy on Iapetus including the effect of Saturn’s eccentricity and Iapetus’ obliquity precession, and evaluating the sublimation rate of H₂O ice from the Iapetus’ surface.As a result, we found that the distribution of the surface albedo changed dramatically after 4.0 Gyr of evolution. The sublimation has three important effects on the resultant surface albedo. First, the albedo in the leading hemisphere has significantly decreased to approach the minimum value. Second, the albedo distribution has been elongated along the equator. Third, the edge of the low albedo region has become clear. Considering the effect of ice sublimation, the current albedo distribution can be reconstructed from the sinusoidal albedo distribution, suggesting the apex-antapex cratering asymmetry as a candidate for the origin of the albedo dichotomy. From the model analysis, we obtained an important aspect that the depth of the turn-over layer where the darkening process proceeded for 4 Gyr should be an order of 10 cm, which is consistent with evaluation from the Cassini radar observations.  相似文献   

Ordovician backarc‐basin metadolerite and metabasalt of the South Kitakami Terrane,Northeast Japan          下载免费PDF全文

Takayuki Uchino  Makoto Kawamura 《Island Arc》2016,25(4):274-286

Basement rocks that occur along the northern margin of the South Kitakami Terrane in Japan consist of Ordovician ultramafic rocks (Hayachine ultramafic complex), gneissose amphibolite (Kuromoriyama amphibolite), and mafic rocks (Kagura igneous rocks, KIR). The KIR are composed of metagabbro, metadolerite, metabasalt, and minor felsic–intermediate dikes. Although the KIR contain green hornblende due to metamorphism of greenschist to epidote–amphibolite facies, they rarely retain primary brown hornblende. Approximately 30% of the metabasalt shows porphyritic textures, with phenocrysts of saussuritized plagioclase and/or altered mafic minerals. The geochemistry of the common metadolerite and metabasalt of the KIR shows a tholeiite trend, a low TiO₂ content, and high Th/Nb and Ti/V ratios. The KIR are therefore indicative of a supra‐subduction zone tectonic setting, which implies a backarc origin (as also indicated by discrimination diagrams). Trace element patterns of the KIR resemble those of the backarc‐basin basalt of the Japan and Yamato basins in the Japan Sea. We propose that the KIR formed during backarc spreading from the Ordovician to Early Silurian. This view is supported by the geochemical data, the tectonic setting of the Hayachine ultramafic rocks, and the provenance of clastics within Silurian sedimentary rocks.  相似文献   

Case study of the transformation of swells propagating into Sendai Bay   总被引：1，自引：0，他引：1  

Yongliang Wei  Hiroshi Kawamura 《Journal of Oceanography》2012,68(1):163-172

A high-resolution two-dimensional map of swell wavelength and propagating direction was retrieved from a phased array type L-band synthetic aperture radar scene observed on 24 September 2006 over Sendai Bay in the Tohoku region of Japan. Features of the wavelength map were compared with a wavelength map calculated from in situ measurements of the swell period using infinitesimal amplitude surface wave theory. The maps corresponded well in most areas, although large differences appeared in the near-shore area (area I) and an area of complicated bottom topography (area II). Because the spatial resolution of swell parameters was too coarse to investigate the surface waves in area I, wavelet transform (WT) was applied along a swell ray to improve the spatial resolution. In the resulting WT wavelength map, the large difference in area I disappeared. For area II, perturbation theory was introduced for surface waves propagating obliquely on a gentle slope. The large wavelength difference in area II was well explained by the second-order solution of perturbation theory.  相似文献