Climate Changes between 25,000 and 6,000 yrs BP Deduced from TOC, TN, and Fossil Pollen Analyses of a Sediment Core from Lake Nojiri, Central Japan.

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  • Kumon Fujio
    Dept. Environmental Sciences, Faculty of Science, Shinshu University
  • Kawai Sayuri
    Dept. Geology, Faculty of Science, Shinshu University
  • Inouchi Yoshio
    Center for Marine Environmental Studies, Ehime University

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Other Title
  • 野尻湖湖底堆積物中の有機炭素・全窒素含有率および花粉分析に基づく約２５０００～６０００年前の気候変動
  • ノジリコ コテイ タイセキブツ チュウ ノ ユウキ タンソ ゼン チッソ ガンユウリツ オヨビ カフン ブンセキ ニ モトヅク ヤク 25 000 6 000ネンマエ ノ キコウ ヘンドウ

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Abstract

Total organic carbon (TOC), total nitrogen (TN), and fossil pollen compositions have been measured at 1- to 2-cm intervals for the upper part of an all-core sample recovered from Lake Nojiri in 1988. TOC and TN contents rapidly increase from the depth zone of 610 to 540cm, with one reversal. The fossil pollen of cool-temperate deciduous trees also becomes abundant around this horizon. Subarctic conifers decrease from 730 to 540cm depth, with some fluctuations.<br>Judging from these results and sediment ages estimated with 14C dates and some marker tephras, the Last Glacial Maximum is reconstructed to have been around 20, 000yrsBP. A warming suggested by increasing fossil pollen of cool-temperate deciduous trees started around 15, 000yrsBP and lasted until about 11, 000yrsBP (about 12, 000calBP), being intercalated with some cooler phases. The warming was especially accelerated around 12, 000yrs BP (14, 000calBP). The cool phases recognized in the Late Last Glacial Age can be compared with the three Dryas periods in Northern Europe by pattern matching, but their ages are older by about 2, 000 to 3, 000 years. This discordance may be a key to understand the mechanism which controls short-term climate changes.<br>A slight cooling phase is also recognized around 9, 000yrsBP. This phase is characterized by decreases in TOC and TN contents, but is not so clearly seen in pollen compositions. This phase may be correlated to the Boreal period in Northern Europe.<br>This study presents the first detailed illustration of climate changes though the termination of the Last Glacial Age in central Japan. The studied core offers a useful standard of climate history, because it can be precisely correlated using the numerous marker tephras.

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