中部山岳地域の湖沼堆積物の有機炭素含有率を指標とした過去16万年間の気候変動復元

A detailed reconstruction of paleoclimate over the past 160 ka has been achieved with a 20-40 year interval, based on the total organic carbon (TOC) and total nitrogen (TN) contents oflake sediments from Lake Nojiri and the Takano Formation, central Japan. The validity of the reconstruction is supported by an analysis of pollen grains from the same sediments. The result represents one of the most detailed and continuous reconstructions of paleoclimate for a land area in Japan during the late Quaternary. The reconstruction provides a key to our understanding of late Quaternary climate in Japan, because the studied sediments contain many widespread tephra marker layers,thereby enabling the correlation of the reconstructed paleoclimate with other areas in and around the Japanese Islands. The TOC content of lake sediment is controlled mainly by the biological productivity of lake water (aquatic organic matter) and the input rate of organic matter from land areas (terrestrial organic matter), as well as the degree of decomposition after deposition. Biological productivity appears to be the main controlling factor in lakes within mid-latitude Japan that contain silt- and clay-rich sediments. Short and long-term fluctuations in TOC are well correlated with the marine δ¹⁸O pattern of SPECMAP and with δ¹⁸O profiles from ice cores in Greenland. The Validity of the paleoclimate reconstructed based on TOC is supported by the results of pollen analysis, although the pollen data have relatively low temporal resolution. Therefore, ln our reconstruction we can identify marine isotope stages (MIS) 1 to 6 and many of the interstadial events recognized in Greenland ice cores. A detailed comparison of the obtained TOC curve with the SPECMAP curve reveals a slight lag in the TOC peaks, which are typically recognized in the MIS 5b and 5d stages. This lag may reflect local factors specific to the Japanese Islands.野尻湖底堆積物および後期更新世高野層のTOC含有率を指標として,過去16万年間の中部山岳地域における気候変動の復元を試みた.まず, TOC含有率の増減が花粉組成の示す寒暖変動で裏付けられており,気候変動の指標として有効であることをそれぞれで確認した.次に,それぞれで標準化したTOC変動曲線を広域テフラDKPを鍵としてつなぎ合わせて,過去16万年間の詳細な変動を復元した. TOCの経年変動は,グリーンランドの氷床が記録する気候変動に匹敵する時間分解能を持ち,その大局的な変動は,海洋酸素同位体比曲線とも対応しており,汎世界的な気候変動を反映している.それを基に陸域の指標テフラを気候編年上に位置づけることができた.解明された詳細な気候変動と指標テフラの枠組みは,列島内の各地の気候変動の対比のみならず,堆積盆の形成や埋積過程,港水準変動の影響などを高精度で解析する上で重要な土台を提供する.Article地質学雑誌 115(7): 344-356(2009)journal articl