Researches in Organic Geochemistry
Online ISSN : 2189-7891
Print ISSN : 1344-9915
ISSN-L : 1344-9915
  • 山本 正伸
    2023 年 39 巻 1 号 p. 1-12
    発行日: 2023/07/14
    公開日: 2023/09/12
    ジャーナル フリー

    Atmospheric carbon dioxide (CO2) is an essential factor in determining the Earth's climate. In predicting future warming, it is necessary to understand how atmospheric CO2 has affected past climate change. Past atmosphericCO2 concentrations have been determined by analyzing gases in ice cores drilled through the Antarctic ice. In this study, we show that the carbon isotope ratios of plant-derived fatty acids in the Bay of Bengal sediments represent past atmospheric CO2 concentration changes by comparing them with those in ice cores. Using this relationship, we have shown for the first time that atmospheric CO2 concentration changes before ca 800,000 years ago can be determined with high precision and high temporal resolution. The results show that even before ca 800,000 years ago, the CO2 concentration fluctuated almost synchronously with the volume of continental ice sheets. However, the CO2 concentrations were unexpectedly not high during the warm period prior to 1 million years ago. It was also found that the CO2 concentrations fluctuated earlier than the volumes of continental ice sheets before 1 million years ago but later than the ice volumes after ca 800,000 years ago.

  • Daochao Xing, Yuko Takizawa, Makio Yanagisawa, Yoshito Chikaraishi
    原稿種別: Articles
    2023 年 39 巻 1 号 p. 13-20
    発行日: 2023/07/14
    公開日: 2023/09/12
    ジャーナル フリー

    Compound-specific isotope analysis of amino acids (CSIA-AA), particularly for nitrogen in muscle tissues of organisms, has been used for identifying the trophic position (TP) of the organisms and the isotope baseline (e.g., the δ values of plants, phytoplankton, etc.) of food webs to illustrate trophic transfer and linkage in ecosystems. However, little is known whether or not other tissues such as scale and blood can be employed as samples for the CSIA-AA. In this study, we compared the tissue-specific δ15N values of amino acids in several aquatic organisms including fish (e.g., for muscle, scale, blood, bone, etc.), gastropods (i.e., for muscle vs. shell protein), and a turtle (i.e., for yolk vs. embryo) to evaluate applicability of these tissues in the CSIA-AA. The results reveal that the δ15N values of amino acids in muscle are substantially identical to those in scale, fin, and yolk of fish as well as in shell protein of gastropods, but not to those in internal tissues (e.g., blood, embryo, etc.). Based on these results, we concluded that the former tissues (e.g., scale and shell) are applicable as alternatives to muscle in the CSIA-AA, whereas the latter tissues are not. We suggest that the latter tissues will be required further evaluation when these tissues are employed as samples in the CSIA-AA.

  • 福地 亮介, 葉田野 希, 朝日 啓泰, 沢田 健
    原稿種別: 論文
    2023 年 39 巻 1 号 p. 21-34
    発行日: 2023/07/14
    公開日: 2023/09/12
    ジャーナル フリー
    J-STAGE Data

    Paleosols are the soils formed on land in the past. Soil profile reflects source materials, microtopography, and climatic and environmental conditions. Although most charactersistics of paleosols have been lost due to erosion and diagenesis, the information for paleoclimatic and paleoenvironmental reconstructions has been recorded in the paleosols. Recently, organic geochemical proxies including biomarkers have been applied to the paleosol study. However, there have been few reports for biomarker variations of paleosols in Japan. The sediment core from Lake Suwa contains some paleosols in lacustrine sediments. The n-alkane proxies such as carbon preference index (CPI) odd to even predominance (OEP) and aquatic plant indicator (Paq) were analyzed. The CPI and OEP values are lower in paleosol layers, but C30 ββ-hopane ratios, a hopanoid biomarker index, are higher. In particular, the CPI values are reversely correlated to the C30 ββ-hopane ratios. From these results, we suggest that n-alkanes with weak odd predominance were presumably derived from plant roots and microbial degradation of long chain, that is odd chain, n-alkanes, and increasing ββ-hopanes, which were fresh biological hopanoids derived from bacteria in the rhizosphere of paleosol layers.