Investigations of causal relationship of lake deepening to increase in diatom cell size

• Project/Area Number: 17K05695
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Stratigraphy/Paleontology
• Research Institution: National Museum of Nature and Science, Tokyo
• Principal Investigator: Megumi Saito-Kato 独立行政法人国立科学博物館, 地学研究部, 研究主幹 (40455423)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000); Fiscal Year 2020: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000); Fiscal Year 2019: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2018: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2017: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000)
• Keywords: 琵琶湖 / 珪藻 / 個体サイズ / 湖水深 / 地球化学分析 / 第四紀 / 氷期間氷期サイクル / 殻サイズ / 古水深 / 後期更新世 / 生産量 / 殻サイズ分布 / 最終氷期 / 完新世 / 形態学的進化 / 大型化 / 水温躍層 / 最終間氷期

Outline of Final Research Achievements

Increase in maximum cell size in Praestephanos suzukii estimated to have occurred in ca. 130-120 ka. Any synchronous changes in lake deepening inferred by a geochemical proxy, As content in Iron hydroxides. Size distribution of P. suzukii has varied in the order of 10,000 or 1,000 years, synchronous with glacial-interglacial cycles during the last 40 ka. Increases of larger cells related to estimated low productivities of P. suzukii and total diatoms in cold phases during the last glacial period, whereas decreases of larger cells to high productivities during Holocene.

Academic Significance and Societal Importance of the Research Achievements

半世紀ものあいだ琵琶湖ボーリングコアを用いた研究が続けられているが、湖内に生息・生育する生物にとって重要な琵琶湖そのものの湖沼学的なパラメータ（例えば、水深、水温、栄養塩濃度など）の変化は十分に明らかにされたとは言いがたい。本研究では過去の水深変化を地球化学的手法で推定することを試みたが、珪藻の大型化とのあいだに単純な関係性は認められなかった。珪藻などのプランクトンにとっては、水深よりむしろ温度躍層の存続期間やその水深が重要な意味を持つことも指摘され、このような湖沼学的なパラメータを過去にさかのぼって明らかにする手法の開発の重要性が再認識された。

Research Products

• [Journal Article] Diatom productivity since the last glacial period using Praestephanos suzukii cell size as supportive evidence (2019)
  • Author(s): Megumi Saito-Kato, Yoshihiro Tanimura, Kazuyoshi Yamada and Keiji Takemura
  • Journal Title: Bulletin of National Museum of Nature and Science, Ser. C Volume: 45 Pages: 49-56
  • Peer Reviewed / Open Access
• [Journal Article] Morphological evolution and changes in geographic distribution of Lake Biwa diatoms in the Quaternary (2018)
  • Author(s): 齋藤めぐみ
  • Journal Title: The Quaternary Research (Daiyonki-Kenkyu) Volume: 57 Issue: 1 Pages: 3-17
  • DOI: 10.4116/jaqua.57.3
  • NAID: 130006402955
  • ISSN: 0418-2642, 1881-8129
  • Peer Reviewed / Open Access
• [Presentation] 珪藻における形態解析の三次元化への挑戦 (2020)
  • Author(s): 齋藤めぐみ・長井裕季子・横山隼
  • Organizer: MRC研究集会ミニ（オンライン）
• [Presentation] 琵琶湖における珪藻の大型化に湖水深の変化は影響したか (2018)
  • Author(s): 齋藤めぐみ・豊田和弘
  • Organizer: 日本古生物学会2018年年会
• [Presentation] Morphological evolution of lacustrine diatoms in Lake Biwa, Japan from a 300 kyr fossil record. (2017)
  • Author(s): Saito-Kato, M. Tanimura, Y., Mori, S. and Julius, Matthew, L.
  • Organizer: InterRad 2017
  • Int'l Joint Research / Invited