Properties and Forming Environment of Humic Acid Pg in the Shimosueyoshi Buried Humic Layer at Oiso Hill, Central Japan.

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  • WATANABE Makiko
    Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Environmental Science and Technology
  • NOZAWA Tomoaki
    Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Environmental Science and Technology
  • HOSONO Mamoru
    Tokyo Nature History Research Structure
  • AOKI Kumiko
    Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Environmental Science and Technology

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  • 大磯丘陵下末吉埋没土層における腐植酸緑色画分Ｐｇの特性と生成環境
  • オオイソ キュウリョウ シモスエヨシ マイボツドソウ ニ オケル フショクサン リョクショク カクブン Pg ノ トクセイ ト セイセイ カンキョウ

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The use of humic acid green fraction (Pg) as a paleoenvironmental indicator still requires integrated case studies applied to tephra and loess soil sequences (Watanabe and Kado, 2000; Watanabe et al., 2001a), as well as biochemical studies on humic acid Pg (Watanabe et al., 2001b). The stability and the chemical transformation of humic acid Pg should be elucidated by investigating paleosols and terrestrial deposits.<BR>This study aims to clarify the properties of humic acid green fraction Pg in the Shimosueyoshi buried layer (SB layer), the buried humic soil originating from tephra supplies of Hakone Caldera, corresponding to Marine oxygen isotope stage 5e. Pg absorption strength (Pg abs), total carbon content (TC), carbon content of extracted humic acid (CHA), pH (NaF) value, major element compositions, and phytolith analyses, together with selective dissolution of Fe compounds, and color measurement according to CIE color system were conducted. The obtained results were : <BR>1) Clear Pg absorption bands at around 450, 570, and 615 nm were detected from all the humic acid of paleosols, corresponding to > 100 ka, located at Oiso Hill, central Japan. The fluctuation of Pg abs of humic acid in the investigated profile showed a significant increase in the SB layer (ca. 130 ka), equivalent to the early stage of MIOS 5e.<BR>2) According to the measurement error of Pg abs determined through the profile, the significant level of Pg abs in this study is confirmed to be much lower than that of Pg abs in previous studies carried on younger tephra soil sequences. It is considered that humic acid Pg is transformed in paleosols over 100 ka.<BR>3) Although the relations among amorphous and crystalline iron hydroxides and Pg absorption strength were not clear in this profile, unlike the previous reports (Kawahigashi et al., 1999, Watanabe and Kobayashi, 2001), the SB layer was characterized by the existence of geothite-like iron hydroxides, suggesting a humid environment.

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