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湖沼堆積物に含まれる脂質化合物の放射性炭素年代測定に関する基礎研究(タンデトロン加速器質量分析計業績報告2006(平成18)年度)

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Abstract

湖沼堆積物中の脂質化合物(脂肪酸、炭化水素等)の放射性炭素年代測定を目的とした基礎実験結果を報告する。標準試料として直鎖状飽和脂肪酸メチルエステル混合物(炭素数16-24)、直鎖状飽和炭化水素 (Octacosane,炭素数28)を用いて、抽出操作前と後での年代値を比較した。直鎖状飽和脂肪酸メチルエステル混合物においては、脂質抽出操作により平均100年程度、^<14>C年代が古くなる結果が得られた。直鎖状飽和炭化水素においてはバックグラウンドに近い値が得られ、脂質抽出操作前と後での^<14>C年代値に差は認められなかった。脂肪酸の年代値が変化した理由として、使用した有機溶媒(ジクロロメタン、メタノール)の調製法の違いによるものと考えられる。\\The age dating and age models for the Late Pleistocene-Holocene studies have mainly progressed by radiocarbon measurements of biogenic materials (total organic carbon (TOC), plant residues, micro fossils) using accelerator mass spectrometry (AMS; Andreev et al., 2001; Yi et al., 2004; Vasi'chuk et al., 2004; Bezrukova et al., 2005). AMS radiocarbon dating is indispensable to perform paleo-environmental, climatic and biological studies. Radiocarbon dating of sedimentary lipids provides relatively accurate age, because total organic carbon (TOC) in the sediments is complex mixture of various organic materials. In this study, we estimate modern and/or dead carbon effect on radiocarbon dating by lipid extraction procedures for lake sediments. For lipids extraction, authentic lipids and wet sediment samples were weighted in 70 ml Teflon centrifuged tubes. 50ml of dichloromethane/methanol (2:1v/v, grade 5000, WAKO) were added in each tubes, then ultrasonicated, shaken with ceramic balls (30 min.) and centrifuged. The supernatant was removed and repeated 3-5 times until the supernatant was colorless. For radiocarbon dating and stable carbon isotope measurements, lipids were combusted at 850℃ for 6 hours in evacuated bycol tubes (9mm x 35 cm) with CuO and Ag wire. The resulting CO_2 was collected and purified in a vacuum line and subsequently reduced to graphite with an iron catalyst and hydrogen at 650℃ for 6h. Radiocarbon measurements were performed by Tandetron accelerator mass spectrometer (Model-4130 AMS, HVEE) at Nagoya University.

タンデトロン加速器質量分析計業績報告 Summaries of Researches Using AMS 2006 (平成18)年度

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