Reconstruction of Holocene climate changes by high resolution analyses of lake sediments

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K16348
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geography
• Research Institution: Ritsumeikan University (2017-2019); Kyushu University (2016)
• Principal Investigator: FUKUMOTO YU 立命館大学, 立命館グローバル・イノベーション研究機構, 研究員 (20772974)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 湖沼堆積物 / 年縞 / 古環境 / 珪藻化石

Outline of Final Research Achievements

This research project aimed to reconstruct climate changes during the Holocene period by analyzing lake sediments retrieved from multiple sites in Finland. Diatom fossils were mainly used for analysis, and I also attempted to make clear the depositional processes of varve layers by observing their sedimentary structure precisely. Results showed unique environmental changes in all analyzed cores in addition to the well-known climate anomalies. Core sediments of Lake Kevo was characterized by thick varve layers deposited by seasonal fluvial activities. Its age model was constructed by varve counting and thin section observation. On the studies of Lake Lehmilampi, climate changes were found to be the main factor affecting the formation of hypoxia and varve formation. Studies on Lake Vesijarvi showed regionally different patterns of diatom assemblages within the same lake basin. All studies showed clear evidences of water pollution by human settlement for the past several centuries.

Free Research Field

古環境学

Academic Significance and Societal Importance of the Research Achievements

気候、環境変動のアーカイブの蓄積のほかに、陸水学や堆積物の研究全般に通ずる基礎資料となるデータが得られた。例えば、気候変動に加え年縞が形成される湖沼周辺の環境条件が明らかになった。また、湖盆全体から複数のコアを採取し分析を行った結果、局所的な違いが顕著にみられ、同じ湖盆でも複数のコア試料の分析が必要であることや、藻類の気候、環境変動に対する応答は物理、化学的な指標とは数十年の時間差があること、つまり藻類特有の緩衝性があることが示された。これらの知見は今後堆積物を採取する際の、湖沼の選定材料として広く使われると考えられ、また湖沼の生態系全体にわたる学術的な価値を有していると考えられる。