5:15 PM - 7:15 PM
[ACC33-P02] Ice core record of 10Be from Dome Fuji reveals variations in the paleointensity of the geomagnetic field and long-term periodicities of solar activity from 200 ka to 240 ka
Cosmogenic 10Be is produced by spallation reactions between galactic cosmic rays and oxygen and nitrogen in the upper atmosphere (Lal and Peters, 1967). Soon after production, 10Be is attached to atmospheric aerosols, and then is deposited on the Earth's surface and is stored in natural archives such as ice cores (Beer et al., 2012). Since the intensity of cosmic rays is negatively related to the intensity of the Earth's and solar magnetic fields, 10Be in ice cores serves as a good proxy for the paleointensity of the geomagnetic field and solar activity.
Here we present a 10Be record from 200 ka to 240 ka with a resolution of approximately 100 years, obtained from the Dome Fuji ice core (the DF2 ice core: Dome Fuji Ice Core Project Members, 2017). The age model of the record is based on the most recent chronology for the Dome Fuji ice cores (DF2021) as constructed by Oyabu et al. (2022).
Pretreatment for 10Be analysis was performed at the Paleoenvironmental and Cosmogenic Nuclide Laboratory of Hirosaki University, followed by 10Be determination using accelerator mass spectrometry at the Micro Analysis Laboratory Tandem Accelerator of the University of Tokyo.
The concentration and flux of 10Be ranged from 14.5 to 16.3 × 104 atoms/g and from 14.7 to 32.8 × 104 atoms/cm2/a, respectively. In the 10Be flux profile, we find three broad increasing peaks centered at 210 ka, 220 ka, and 240 ka, which are probably associated with the increases in cosmic ray flux due to the geomagnetic excursions at these times. We also find centurial to millennial periodicities superimposed on the broad 10Be flux variations. These may correspond to the Eddy and Suess cycles of solar activity found in the Holocene cosmogenic nuclide records (10Be and 14C) (e.g. Usoskin et al., 2023).
Here we present a 10Be record from 200 ka to 240 ka with a resolution of approximately 100 years, obtained from the Dome Fuji ice core (the DF2 ice core: Dome Fuji Ice Core Project Members, 2017). The age model of the record is based on the most recent chronology for the Dome Fuji ice cores (DF2021) as constructed by Oyabu et al. (2022).
Pretreatment for 10Be analysis was performed at the Paleoenvironmental and Cosmogenic Nuclide Laboratory of Hirosaki University, followed by 10Be determination using accelerator mass spectrometry at the Micro Analysis Laboratory Tandem Accelerator of the University of Tokyo.
The concentration and flux of 10Be ranged from 14.5 to 16.3 × 104 atoms/g and from 14.7 to 32.8 × 104 atoms/cm2/a, respectively. In the 10Be flux profile, we find three broad increasing peaks centered at 210 ka, 220 ka, and 240 ka, which are probably associated with the increases in cosmic ray flux due to the geomagnetic excursions at these times. We also find centurial to millennial periodicities superimposed on the broad 10Be flux variations. These may correspond to the Eddy and Suess cycles of solar activity found in the Holocene cosmogenic nuclide records (10Be and 14C) (e.g. Usoskin et al., 2023).