2023 Fiscal Year Final Research Report

Natural remanent magnetization by magnetotactic bacteria - approaching the reliability of paleomagnetic records through replication experiments

Research Project

PDF

Project/Area Number	18K18789
Research Category	Grant-in-Aid for Challenging Research (Exploratory)
Allocation Type	Multi-year Fund
Review Section	Medium-sized Section 17:Earth and planetary science and related fields
Research Institution	Kochi University
Principal Investigator	YAMAMOTO YUHJI 高知大学, 教育研究部総合科学系複合領域科学部門, 教授 (00452699)
Co-Investigator(Kenkyū-buntansha)	諸野祐樹国立研究開発法人海洋研究開発機構, 超先鋭研究開発部門(高知コア研究所), 上席研究員 (30421845) 山崎俊嗣東京大学, 大気海洋研究所, 教授 (80344125)
Project Period (FY)	2018-06-29 – 2024-03-31
Keywords	磁性細菌 / 残留磁化 / 古地磁気強度
Outline of Final Research Achievements	Using magnetotactic bacteria cells, a group of samples for magnetic measurement was prepared through analog experiments simulating the “early stages of sediment formation”. The properties of the acquired natural remanent magnetization (NRM) and the relative paleomagnetic intensity (RPI) index were considered. In the sample group in which the cells were highly efficiently oriented in response to the applied magnetic field, the NRM intensity increased nonlinearly in accordance with the tanh function as the applied magnetic field strength increased. On the other hand, in the sample group with low efficiency orientation, the NRM intensity increased linearly with the increase in the applied magnetic field intensity. The RPI index also tended to approach the values reported for actual natural marine sediments, suggesting that biological disturbance processes after initial deposition may be important in the magnetization acquisition mechanism of biogenic magnetite.
Free Research Field	古地磁気学・岩石磁気学
Academic Significance and Societal Importance of the Research Achievements	地球システム進化を探るうえで，海底堆積物のNRMから推定できる古地球磁場の情報は重要である。このNRMは，磁性細菌に起源をもつ生物源磁鉄鉱にも担われているが，NRMの獲得過程や，獲得されるNRMの性質については未解明の部分が多い。本研究では，実際に磁性細菌の細胞を用いて，生物源磁鉄鉱がNRMを獲得する過程のアナログ実験と磁気分析を行い，獲得される残留磁化の性質を検討した。その結果，改めて，実際の天然堆積物のNRM獲得過程では，生物の活動によって磁性粒子が擾乱される過程が重要であることが認識されるなど，信頼性の高い古地球磁場情報の推定に資する成果が得られた。