Cosmogenic Be-10 in ice cores has been investigated for elucidating historical cosmic-ray modulation by solar-geomagnetic field variations. Evidences of 11-yr and 200-yr solar cycles were found in the Be-10 profiles of ice cores from Greenland (Beer et al., 1988, 1990; Finkel and Nishiizumi, 1997) and Antarctica (Raisbeck et al., 1990; Steig et al., 1996; Bard et al., 1997). Besides C-14 in tree rings, Be-10 in ice cores is thought as a proxy indicator of solar activity at least in the Holocene epoch (e.g. Usoskin et al., 2004). The problem that should be considered when we apply Be-10 for such studies is contamination of local meteorological signals. Thus, comparing Be-10 records from different ice cores is important, even if those are retrieved from the same polar region.
In this paper, we present a short (1500-1800 yr A.D.) Be-10 record obtained from an ice core retrieved from Dome Fuji station, Eastern Antarctica (77° 19' S, 39° 42' E). About 200 g of ice was melted by using a microwave oven, followed by adding 0.1 mL of HNO3, 0.3 mg of Be-9 carrier, and 0.1 mg of Al-27 carrier. Cation exchange separation was then performed to isolate the beryllium fraction. Be(OH)2 was precipitated by adding NH4(aq.) to the purified solution; this was then converted to BeO by heating in an electric furnace. Be-10 measurements were performed by using MALT-AMS system at the University of Tokyo.
The Be-10 concentrations range between 70,000 and 130,000 atoms g-1, and are about two times higher than those of the South Pole record (Raisbeck et al., 1990; Bard et al., 1997). An increased peak of the concentrations is found from 1645 to 1715 yr A.D., coinciding with the most famous solar-activity minimum: Maunder Minimum. High Be-10 concentrations are also found before 1540 yr A.D. and near 1800 yr A.D., apparently corresponding to Spörer and Dalton minima, respectively. Similarity of the Be-10 profiles of the Dome Fuji and the South Pole records is high, but the former appears more similar in shape to the delta-C-14 profile obtained from tree rings. This would mean that meteorological disturbance is weaker at the Dome Fuji station; this interpretation would be supported by the higher Be-10 concentrations (i.e. lower snow accumulation rates) observed in the Dome Fuji record. The Be-10 record from Dome Fuji station and its stacking with those from different stations would be advantageous to investigating the past solar activity.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)