4:00 PM - 4:15 PM
[HQR06-03] ESR analysis of aeolian dust quartz in tephric loess sequences
Keywords:Quartz, dust, climate change, ESR
While temperature changes during the glacial-interglacial cycles of the Quaternary period have been studied in detail, it is difficult to investigate the direction and intensity of the winds such as monsoons. To address this issue, the particle sizes and the electron spin resonance (ESR) signal were investigated, the latter of which has been shown to be a good proxy for determining the dust source [1] . Although the previous studies investigated the temporal variation of the sources over the last 150,000 years with using marine sediments, terrestrial sedimentay sequences would have advantage for studies on short timescale variation as they have a fast sedimentation rate. In the present study, we focused on tephric loess sequences distributed over land with a high deposition rate, and investigated temporal changes in the number of oxygen vacancies in quartz in the samples of the sequences.
We analyzed the samples in the loess sequence at the Kamiyoshida outcrop in Rokunohe Town, Aomori Prefecture. The 61 samples were continuously collected every 5 cm in a range 110 cm to 420 cm deep from the surface. Size fractions from 2 to 20 μm and from 20 to 50 μm were extracted by the Stokes method, and quartz was extracted by chemical treatments. Silicon was mixed into the sample and XRD analysis was performed to determine the exact quartz content in the extracted sample. The number of oxygen vacancies in quartz was measured by electron spin resonance from the signal intensity the E1' center. The signal intensity is larger in the uppermost 115cm to 120cm range. Estimating the age of this stratigraphy based on tephra and coastal terraces, this range would likely correspond to the coldest period of the last glacial period. These results suggest that the ESR signal (the number of oxygen vacancies estimated from the signal intensity of the E1' center) would be a good proxy in investigating the climate change in Quaternary with high temporal resolution.
[1] Nagashima et al. (2007) Geochemistry, Geophysics, Geosystems., 8, Q02Q04
We analyzed the samples in the loess sequence at the Kamiyoshida outcrop in Rokunohe Town, Aomori Prefecture. The 61 samples were continuously collected every 5 cm in a range 110 cm to 420 cm deep from the surface. Size fractions from 2 to 20 μm and from 20 to 50 μm were extracted by the Stokes method, and quartz was extracted by chemical treatments. Silicon was mixed into the sample and XRD analysis was performed to determine the exact quartz content in the extracted sample. The number of oxygen vacancies in quartz was measured by electron spin resonance from the signal intensity the E1' center. The signal intensity is larger in the uppermost 115cm to 120cm range. Estimating the age of this stratigraphy based on tephra and coastal terraces, this range would likely correspond to the coldest period of the last glacial period. These results suggest that the ESR signal (the number of oxygen vacancies estimated from the signal intensity of the E1' center) would be a good proxy in investigating the climate change in Quaternary with high temporal resolution.
[1] Nagashima et al. (2007) Geochemistry, Geophysics, Geosystems., 8, Q02Q04