11:00 AM - 1:00 PM
[SEM15-P05] Rock magnetic investigations on magnetic properties of samples including extracted magnetotactic bacteria and their contribution to magnetic properties of sediments
Keywords:magnetotactic bacteria, magnetic property, sediments
In order to investigate magnetic contribution of magnetotactic bacteria to magnetic properties of sediments, we performed the following two experiments on lake sediments in Rokusen Ike, Toyama City:
We corrected topmost sediments with an Ekman-Birge grab and sediment core of about 15 cm long with a HR-type core sampler. We extracted magnetotactic bacteria from the topmost sediments with small magnets. Samples with extracted bacteria and water were dried in a refrigerator. The core sample was sliced at 1cm interval, and each slice was freeze-dried. Rock magnetic analyses were performed on samples including extracted magnetitactic bacteria (sample-MB) and freeze-dried sediment powders.
Results from rock magnetic experiments showed the existence of magnetite or maghematized magnetite with a small amount of hematite in the sediments. Magnetic hysteresis ratios of the sediments and sample-MB were plotted in the range of pseud-single domain. Results from analyses of coercivity distribution on acquisition curves of isothermal remanence showed the existence of two different components with mean fields (MFs) of about 30 and 70 mT in sample-MB and four components in the sediment samples. IRM intensities of two components with similar MF to the two components of sample-MF were about 70% of the total IRM.
(B) We corrected two sediment cores with the bottom water by a HR-type core sampler. We kept the content of dissolve oxygen in water above sediment for the two cores constant in an oxygen-rich and an oxygen-poor conditions, respectively. We sampled sub cores form the two cores after about three weeks and six weeks, and freeze-dried sediment powders from the sub cores were analyzed.
Although soil colors of top sediments (0~3 cm in depth) in the cores changed, magnetic properties showed no remarkable changed. Coercivity distributions in IRM acquisition curves did not show any significant changes.
We corrected topmost sediments with an Ekman-Birge grab and sediment core of about 15 cm long with a HR-type core sampler. We extracted magnetotactic bacteria from the topmost sediments with small magnets. Samples with extracted bacteria and water were dried in a refrigerator. The core sample was sliced at 1cm interval, and each slice was freeze-dried. Rock magnetic analyses were performed on samples including extracted magnetitactic bacteria (sample-MB) and freeze-dried sediment powders.
Results from rock magnetic experiments showed the existence of magnetite or maghematized magnetite with a small amount of hematite in the sediments. Magnetic hysteresis ratios of the sediments and sample-MB were plotted in the range of pseud-single domain. Results from analyses of coercivity distribution on acquisition curves of isothermal remanence showed the existence of two different components with mean fields (MFs) of about 30 and 70 mT in sample-MB and four components in the sediment samples. IRM intensities of two components with similar MF to the two components of sample-MF were about 70% of the total IRM.
(B) We corrected two sediment cores with the bottom water by a HR-type core sampler. We kept the content of dissolve oxygen in water above sediment for the two cores constant in an oxygen-rich and an oxygen-poor conditions, respectively. We sampled sub cores form the two cores after about three weeks and six weeks, and freeze-dried sediment powders from the sub cores were analyzed.
Although soil colors of top sediments (0~3 cm in depth) in the cores changed, magnetic properties showed no remarkable changed. Coercivity distributions in IRM acquisition curves did not show any significant changes.