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Volume 40 (2006)
- Issue 4 Pages 263-
- Issue 3 Pages 111-
- Issue 2 Pages 33-
- Issue 1 Pages 1-
Volume 40, Issue 4
Displaying 1-7 of 7 articles from this issue
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Reviews
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Tamano OMATA, Atsushi SUZUKI, Hodaka KAWAHATA, Tadashi MARUYAMA2006 Volume 40 Issue 4 Pages 263-276
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSCarbon and oxygen stable isotope ratios of coral skeletons are widely measured and discussed as environmental proxies. Coral skeleton contains less oxygen-18 and carbon-13 compared to the expected values for isotopic equilibrium with ambient seawater. While oxygen isotope ratio is mainly controlled by seawater temperature and salinity, an interpretation of carbon isotope variation is complicated. Carbon isotope ratio is considered to correlate to light intensity through the metabolic reactions of coral-algae symbiotic system. However, a few models for carbon isotope fractionation are proposed. In the process of coral skeletal formation, kinetic isotope effects are also shown to be an important factor, controlling isotopic fractionation. Because kinetic and metabolic isotope effects cause carbon isotopic fractionation in nearly opposite direction, they diminish each other and make interpretation of the isotopic records complicated. The main objective of this study is to review recent studies, which proposed models of stable carbon isotope variations relating to kinetic and metabolic isotope effects of coral skeleton.View full abstractDownload PDF (1777K) -
Kosei E. YAMAGUCHI2006 Volume 40 Issue 4 Pages 277-286
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSIron-bearing carbonate minerals such as siderite (FeCO3) have formed throughout the Earth's history. However, its formational mechanism, in particular pathway (s) of Fe incorporation into carbonate crystals, have not been well constrained. Recent studies have demonstrated that large fractionations of stable Fe isotopes occur during biogeochemical redox cycling (Fe3+ ⇄ Fe2+). Therefore, Fe isotope (bio) geochemistry is potentially useful, when applied to the Fe-carbonate system, to understand the (bio) geochemical behavior of Fe during Fe-carbonate formation in sediment diagenesis and to constrain its depositional environment. In this contribution, the current progress of Fe isotope geochemistry for the Fe-carbonate system is summarized using examples from experimental studies and from field studies of Cretaceous, Jurassic, and Archean carbonate rocks. Future studies of Fe isotope geochemistry of carbonate rocks are proposed, with new hypotheses for the Neoproterozoic "Snowball Earth" and stromatolites. Experimental determination of essential isotope fractionation factors between different Fe-bearing carbonate minerals and between Fe-bearing minerals and Fe-bearing fluids are needed for better interpretation of field data. Despite its infancy, Fe isotope biogeochemistry will be a promising new tool for the studies of the Fe-carbonate system.View full abstractDownload PDF (1859K) -
Kazuyuki YAMAMOTO, Yasufumi IRYU, Tsutomu YAMADA2006 Volume 40 Issue 4 Pages 287-300
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSCarbon and oxygen isotopic compositions of brachiopod shells have been used for the reconstruction of Paleozoic global carbon cycles and seawater temperatures. Brachiopods occur throughout the Phanerozoic and their secondary shell layer consists of low-magnesium calcite. It is assumed that the shells were precipitated in isotopic equilibrium with ambient seawater. Recent studies, however, showed that isotopic composition of secondary shell layer varies due to "vital effects" and that the criteria proposed in previous studies to distinguish the diagenetic alteration of fossil brachiopod shells are not always perfect. In order to increase the reliability of the isotopic composition of brachiopod shells as a proxy for ancient seawater conditions, it is necessary to clarify variations in isotopic composition in a single shell and within and between species by studying modern brachiopods and to compare the variations to the measured environmental conditions such as temperature, salinity, and isotopic composition of seawater. This will allow selection of species and shell portions that best reflect the isotopic composition of ambient seawater. The information about shell ultrastructure, isotopic and trace elemental compositions of modern specimens are also needed to quantify the degree of modification of original isotopic composition resulting from diagenetic alteration by examining fossil forms.View full abstractDownload PDF (2203K)
Original papers
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Tomoaki TSUNODA, Hodaka KAWAHATA, Atsushi SUZUKI, Kayo MINOSHIMA, Naot ...2006 Volume 40 Issue 4 Pages 301-311
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSPrecise and long term climate data are necessary to predict the magnitude of climate change in the future. The tropical regions are important subsystem of the global climate system because it receives over 50% of total amount of solar energy to the earth. Climate data, however, are available only for recent about 30 years. Thus climate reconstruction with proxies is urgently required. We conducted oxygen isotope analysis of the latest 30 years part of a 272 cm-long core of annually banded coral Porites sp. from Ishigaki Island, the Ryukyus, Japan to reconstruct sea surface temperature (SST) of the region. Significant correlation between coral skeletal oxygen isotope ratio and winter SST allow precise estimate of winter-time SST of the region. In the first half of the period, the winter SST of Ishigaki Island was strongly correlated to the development of winter Asian monsoon. After the climate regime shift in 1988/1989 at middle latitude Pacific, it showed no correlation to the monsoon and instead the influence of Kuroshio Current was suggested. Winter-time climate mechanism of the Ryukyu Islands region has changed since the regime shift. Further reconstruction of SST based on coral records at Ishigaki Island will greatly contribute to understand the climate system of the northern hemisphere.View full abstractDownload PDF (1507K) -
Masae HASEGAWA, Keiji USUI, Haruo SHINDO2006 Volume 40 Issue 4 Pages 313-321
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSIt has been assumed that the metal complexing abilities of fulvic acids, which are one of the humic substances, play an important role for phosphorus releasing from sediments under aerobic condition in shallow lakes and internal bay. However, little information is available on the nature, properties, and structures of fulvic acids which can promote the phosphorus releasing from calcium phosphates in the sediments. In this study, fulvic acids extracted from 3 lake sediments were divided into hydrophilic and hydrophobic fractions with Amberlite XAD-2 resin, and then these fractions were subjected to a molecular weight fractionation by Sephadex G-15 gel. The calcium complexing abilities of the fractions obtained were examined by the reaction chromatography using a Ca-saturated gel column. Both hydrophilic and hydrophobic fractions displayed the calcium complexing abilities at the low molecular weight fractions (less than 1,500 D). The abilities of the former fractions were 2.5 times higher than those of the latter fractions at a maximum level.View full abstractDownload PDF (902K)
Abstract of doctoral thesis
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Yukio Yamamoto2006 Volume 40 Issue 4 Pages 322-
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSDownload PDF (203K) -
Yumiko Watanabe2006 Volume 40 Issue 4 Pages 323-
Published: December 26, 2006
Released on J-STAGE: January 27, 2017
JOURNAL FREE ACCESSDownload PDF (208K)
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