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モンゴル・フブスグル湖から採取された81mドリリングコア試料 (HDP04)の放射性炭素年代測定(2)(タンデトロン加速器質量分析計業績報告2005(平成17)年度)

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Abstract

古環境変動解析を目的として、モンゴル・フブスグル湖から 81mの柱状堆積物(試料名、HDP04)が2004年に採取された。HDP04試料(Core1-1からCore3-1、深さ0-242cm)の放射性炭素年代測定結果を名古屋大学加速器質量分析計業績報告書(XVI)において報告した(渡邊ら、2005)。Core1-1は試料採取時における堆積層の撹乱を示す結果が得られ、Core3-1(深さ211cm)では深度方向に対する^<14>C年代値の逆転が認められた。今回は Core3-1における年代値の逆転について、より詳細な情報を得るために、末測定層8試料(Core2-Core5、深さ0-501cm)の年代測定結果を報告する。Core2-1の^<14>C年代値は深さとともに古くなり、堆積速度(5.3cm/kyr)は既報の値とほぼ一致した。 Core3-1からCore5-1(深さ211-501cm)の^<14>C年代値の変化から、Core3-1上部はフブスグル湖底堆積物表層に一致することが示唆された。\\Lake Hovsgol is located in northern Mongolia and at a high elevation (1645m above sea level). This geographical characteristic makes Lake Hovsgol a unique place for paleoclimate studies using a continuous core sediment. Analyses of organic and inorganic components have been carried out using short cores (core length; 1-2m) from Lake Hovsgol [Fedotov et al., 2004; Karabanov et al, 2004; Nara et al., 2005]. In 2004, a drilling core (HDP04) and gravity core (GC-4) were taken from the basin floor of Lake Hovsgol (50°57'19"N, 100°21'32"E; water depth, 250m). The lengths of the HDP04 and GC-4 sediment cores were ca. 81m and 0.6m, respectively. Radiocarbon age dating for the latest Quaternary was performed for the 26 samples (total organic materials) from the upper part of the HDP04 sediment cores (〜500cm depth) and the gravity core by an accelerator mass spectrometer (Model-4130 AMS, HVEE). In the HDP04 Core2 sediment sample, ^<14>C ages of the layers on 0.5 and 70.5 cm in depth are ca. 4.1 and 17.3 kyrBP, respectively. However, the ^<14>C age of ca. 4.7 kyrBP is obtained at the top of Core3 (211.5 cm in depth). The top of Core3 (200cm in depth) may be consistent with the surface layer of Lake Hovsgol sediment. The ^<14>C age of moss fragment in Core4 (18.7 kyrBP, 353.5 cm in depth) is younger than that of TOC (23.8 kyrBP). Changes for ^<14>C ages in the HDP04 sediment cores are not coincident with previous studies on other Lake Hovsgol sediment cores. The sediment layers below 2m in depth for HDP04 cores are available to environmental and biological investigations, because the ^<14>C age becomes older with depth, and changes of the ^<14>C age are consistent with previous studies.

タンデトロン加速器質量分析計業績報告 Summaries of Researches Using AMS 2005 (平成17)年度

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