Calibration and validation of the ocean color version-3 product from ADEOS OCTS     

Masanobu Shimada  Hiromi Oaku  Yasushi Mitomi  Hiroshi Murakami  Akira Mukaida  Yasuhisa Nakamura  Joji Ishizaka  Hiroshi Kawamura  Tasuku Tanaka  Motoaki Kishino  Hajime Fukushima 《Journal of Oceanography》1998,54(5):401-416

We present calibration and validation results of the OCTS’s ocean color version-3 product, which mainly consists of the chlorophyll-a concentration (Chl-a) and the normalized water-leaving radiance (_nL_w). First, OCTS was calibrated for the inter-detector sensitivity difference, offset, and absolute sensitivity using external calibration source. It was also vicariously calibrated using in-situ measurements for water (Chl-a and_nL_w) and atmosphere (optical thickness), which were acquired synchronously with OCTS under cloud-free conditions. Second, the product was validated using selected 17 in-situ Chl-a and 11 in-situ_nL_w measurements. We confirmed that Chl-a was estimated with an accuracy of 68% for Chl-a less than 2 mg/m³, and_nL_w from 94% (band 2) to 128% (band 4). Geometric accuracy was improved to 1.3 km. Stripes were significantly reduced by modifying the detector normalization factor as a function of input radiance.  相似文献   

MicroRaman spectroscopy of anomalous planar microstructures in quartz from Mt. Oikeyama: Discovery of a probable impact crater in Japan     

Masao SAKAMOTO  Arnold GUCSIK  Hirotsugu NISHIDO  Kiyotaka NINAGAWA  Tasuku OKUMURA  Shin TOYODA 《Meteoritics & planetary science》2010,45(1):32-42

Abstract– Planar deformation features (PDFs) and planar fractures (PFs) have been found and confirmed by optical microscope observations and microRaman spectroscopy in quartz grains from Mt. Oikeyama (Akaishi Mountains, Central Japan), for which the semicircular topographic feature of the ridge suggests a crater formed by an impact event. According to the optical microscope observations, a low shock pressure (8–10 GPa) is estimated by the occurrence of basal or ω PDFs leading to lack of multiple sets of PDFs. In addition, a new type of planar microstructure was found in several quartz grains. The microRaman characteristics of PDFs in quartz from Mt. Oikeyama show the amorphous state indicating the presence of weak broad bands at 400 and 800 cm^?1 peak positions. These characteristics are indicative of PDFs that are limited to shocked quartz. This indicates an impact origin for distinct planar microstructures in quartz from Mt. Oikeyama.  相似文献   

Geometric Series-Steady State (GSSS) Model: A New Protocol for Interpreting Compound-Specific Δ14C Data     

Tasuku Akagi 《Mathematical Geosciences》2012,44(7):843-861

A model system developed to understand the complicated history of general organic matter in soil using its carbon isotopic data such as ??¹⁴C and ?? ¹³C is described. The system, named the geometric series-steady state (GSSS) model, is mathematically described as when the geometric series reaches a steady state in infinite time. This model assumes that molecules of photosynthetic origin are continuously supplied as well as decaying at constant rates. Consideration of the model leads to the following general remarks: (1) the GSSS model defines the unique undisturbed line on the ??¹⁴C age-abundance plane, along which any molecules supplied exclusively by photosynthesis may fall; (2) the model defines the disturbed regions on the plane: molecules supplied by not only photosynthesis but also biotic/abiotic synthetic reactions may give plots on the disturbed regions; (3) the ?? ¹³C value of a molecule cannot be fractionated by Rayleigh distillation type-fractionation. As an exercise, the GSSS model has been applied to the reported data of several fatty acids of different carbon number from soil. A protocol is presented which applies the GSSS model to the natural system, whose ??¹⁴C value was greatly altered by the bomb effect. By the combination of the GSSS consideration and model simulation using real atmospheric ¹⁴C data during the last half century, the author investigated the behavior of fatty acids within the assumptions of the model. Assuming that fatty acids with carbon number greater than or equal to 26 are undisturbed, the GSSS model concludes that fatty acids in soil with carbon number less than 26 are not directly supplied from leaf litter, but should be synthesized continually from other less labile molecules in the soil. The proportion of synthesized molecules to those supplied originally from leaves is greater for the smaller carbon numbered fatty acids. The GSSS model should be applicable to any system, in which a molecule is regularly supplied from atmospheric CO₂ via photosynthesis.  相似文献   

Inhibiting effects of lanthanum ion on calcite formation from CaCL2-NaHCO3 solutions at 25°C     

Tasuku Akagi  Yuhi Kono 《Aquatic Geochemistry》1995,1(2):231-239

The influence of La³⁺ on calcite formation was studied using CaCl₂-NaHCO₃ solutions. We adopted a closed system, where the pH change of the solutions was monitored in a closed vessel. The closed system reduces a number of thermodynamic variables of the solution, thus enabling us to calculate the amount of CaCO₃ precipitate only from pH with the assumption of equilibria among dissolved components in solution. After the analytical inspection of the calculation and assumption on which the calculation is based on, it was applied to experiments of the calcite formation in a Teflon vessel. The mole concentration of lanthanum added in the experiments was smaller than 1/3000 of that of calcium ion in the solutions. The addition of lanthanum oxide, chloride, and nitrate caused the difference in the pH change of the solution. The decrease of pH was smaller when lanthanum reagents were added, indicating that the amount of CaCO₃ precipitate decreased. The smallest decrease was observed when lanthanum chloride or nitrate salt was added. The X-ray diffraction study showed that the CaCO₃ precipitated in any solutions were calcite. If an equilibrium is assumed, which is considered to be likely from the pH change, the ion activity product (IAP) calculated in this study increased about 6 times when lanthanum ion, whose concentration is only 1/14 000 mole of calcium ion, was present.  相似文献   

Intergranular trace elements in mantle xenoliths from Russian Far East: Example for mantle metasomatism by hydrous melt     

Junji  Yamamoto  Shun'ichi  Nakai  Koshi  Nishimura  Ichiro  Kaneoka  Hiroyuki  Kagi  Keiko  Sato  Tasuku  Okumura  Vladimir S.  Prikhod'ko  Shoji  Arai 《Island Arc》2009,18(1):225-241

Based on both major and trace element chemistry, the occurrence of the intergranular component in mantle-derived xenoliths from far eastern Russia has been constrained. Whole-rock trace element measurements of one xenolith show apparent negative anomalies in Ce, Th, and high field strength elements on normalized trace element patterns. The trace element pattern of the whole rock differs from those of constituent minerals, indicating that the anomalies in the whole rock are attributable to the presence of an intergranular component. That assumption was confirmed using in situ analysis of trace elements in the intergranular substance and melt inclusion using laser ablation inductively coupled plasma–mass spectrometry. Both the intergranular component and the melt inclusions have identical trace element patterns, which mean that these materials are a cognate metasomatizing agent. The anomalies are regarded as mantle metasomatism related to an aqueous fluid. Hydrous minerals were observed on the wall of the melt inclusions using micro-Raman spectroscopy, indicating that the melt inclusions contained a large amount of water. Thus, this study reveals a trace element composition of a hydrous metasomatizing agent in the mantle.  相似文献   

Bacterial symbiosis forming laminated iron‐rich deposits in Okuoku‐hachikurou hot spring,Akita Prefecture,Japan     

CHIZURU TAKASHIMA  TOMOYO OKUMURA  SHIN NISHIDA  HIROKO KOIKE  AKIHIRO KANO 《Island Arc》2011,20(2):294-304

Banded iron formations are the most characteristic of Archean–Paleoproterozoic sediment records. Laminated textures resembling banded iron formations can be observed in modern hot‐spring environments. Using sedimentological and microbiological techniques, we investigated the processes of laminar formation and considered the origin of lamination textures. An iron‐rich deposit at the Okuoku‐hachikurou hot spring in Japan exhibits sub‐millimeter laminations consisting of bacteria‐induced ferrihydrite and aragonite. The ferrihydrite particles are spherical and exhibit fine lamination, up to 100 µm thick in ferrihydrite‐rich parts. In aragonite‐rich parts, ferrihydrite particles form filamentous textures with diameters of 10–30 µm, but not laminations. Textural analysis using scanning electron microscopy and phylotype analysis using 16S rRNA indicated the bacterial contribution to ferrihydrite precipitation. A sheath‐like fabric showing a meshwork of nanometer‐order organic filaments, and sheath‐forming bacteria were observed in the deposit specimen etched by citric acid. Phylotype analysis detected in the iron‐rich deposits some bacterial types related to cyanobacteria, purple bacteria, and iron‐oxidizing bacteria. Iron‐oxidizing bacteria probably were responsible for precipitation of the ferrihydrite. Chemolithoautotrophic iron‐oxidizing bacteria are microaerophilic and thrive on Fe(II) in a redox gradient, but dissolved oxygen was not detected in the Okuoku‐hachikurou hot spring. Thus, a certain supply of oxygen is needed for metabolism of the microaerophilic iron‐oxidizing bacteria. The distribution of photosynthetic pigments in the iron‐rich parts indicates that the most likely source of oxygen is photosynthesis by cyanobacteria. This symbiotic relationship between cyanobacteria and iron‐oxidizing bacteria can explain the laminated texture of iron‐rich deposits in the Okuoku‐hachikurou hot spring. These laminations may reflect changes in photosynthetic intensity. There is presently some debate about the bacterial groups that may have played roles in precipitation of banded iron formations. This study presents a new bacterial model for iron precipitation and may provide a mechanism for sub‐millimeter laminations in banded iron formations deposited in shallow water.  相似文献   

Composition of rare earth elements in settling particles collected in the highly productive North Pacific Ocean and Bering Sea: Implications for siliceous-matter dissolution kinetics and formation of two REE-enriched phases     

Tasuku Akagi  Feng-fu Fu  Kozo Takahashi 《Geochimica et cosmochimica acta》2011,75(17):4857-4876

Settling particles were sampled monthly for 1 year using an automated time-series sediment trap positioned at similar depths at two sites of high diatomaceous productivity in the North Pacific Ocean and Bering Sea. The particles were analyzed for rare earth elements (REEs) by inductively coupled plasma mass spectrometry (ICP-MS) with and without chemical treatment of the bulk samples to isolate siliceous fractions. The REE composition of the bulk samples is explained largely by the contribution of two distinct components: (i) carbonate with a higher REE concentration, a negative Ce anomaly and lighter REE (LREE) enrichment; (ii) opal with a lower REE concentration, a weaker negative Ce anomaly and heavier REE (HREE) enrichment.The siliceous fractions of settling particles are characterized by high Si/Al ratios (30-190), reflecting high diatom productivity at the studied sites. The La/Al ratio of the siliceous fraction is close to that of the upper crust, but the Lu/Al and Lu/La ratios are significantly higher than those of the upper crust or airborne particles, indicating the presence of excess HREEs in the siliceous fraction. Diatoms are believed to be important carriers of HREEs.The Ce anomaly, Eu anomaly, slope of the REE pattern, and ΣREE of the siliceous fraction vary exponentially with decreasing total mass flux. They can be well-reproduced according to the differential dissolution kinetics of elements in the order of Ce < lighter REEs (LREEs) < Eu = heavier REEs (HREEs) < Si from settling particles, where the dissolution rate is critically reduced through particle aggregation. This order is consistent with the vertical distribution of dissolved REEs and Si in oceans. The differential dissolution kinetics leads to HREE enrichment of the original diatoms and REE enrichment of dissolved diatoms. The Lu/Si ratio of the siliceous fraction of settling particles recovered from some of the highest diatom fluxes is identical to that of the two elements dissolved in deep seawater, providing further evidence for the dissolution of siliceous matter in deep water.  相似文献   

琵琶湖中浊度的季节变化     

远藤修一  Kunihiko SAGI  Naonori FUKUYAMA  Munetsugu KAWASHIMA  奥村康召 《湖泊科学》1998,10(S1):267-273

Seasonal variation of the turbidity (suspended substance) has been investigated in Lake Biwa. During the last five years, vertical and horizontal distributions of water temperature, turbidity, electric conductivity and chlorophyll-a have been obtained both in the south basin and the southern part of the north basin of Lake Biwa. The benthic nepheloid layer (BNL) developed in the seasons of thermal stratification, and is not detectable in the non-stratification period (winter). The BNL is mainly maintained by the organic matter such as phytoplankton under decomposition. However, the turbidity in the nepheloid layer was much affected by the turbid water from rivers after heavy rainfall. In this case, the major component of the suspended substance (SS) in the nepheloid layer was inorganic soil. The particulate P concentration, which is originated from phytoplankton, also increased after a rain fall. This suggests that phytoplankton in the surface layer sinks with clay and silt coming through rivers. From summer to the end of the stratification period, another kind of turbidity appeared in the bottom layer. This is caused by the chemical reaction of manganese under the anoxic condition. The resuspension of bottom sediment by strong currents also occurred, but it is not a major process for maintaining the BNL.  相似文献