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Cosmogenic nuclides contained in the annual layers of natural materials record temporal variations in the galactic cosmic ray flux. 14C in tree rings and 10Be in ice cores from polar regions are often used to retrieve accurate histories of galactic cosmic rays. However, the variation in 14C produced in the atmosphere is strongly attenuated in the carbon cycle and the amplitude of decadal scale variations in tree rings is approximately 0.2‰. In the case of 10Be in ice cores, the variation remains at a relatively large amplitude; however, the records are accompanied by dating uncertainties. Another material that contains 10Be is sediment in continental areas. Terrestrial carbonate deposits sometimes form clear annual layers; however, detailed analyses on such deposits have not yet been widely conducted. Therefore, we evaluate the possibility of retrieving information concerning the galactic cosmic ray flux from the terrestrial carbonate deposits. In this paper, we report our preliminary results obtained from the measurements of 10Be in travertine and tufa samples from South China. We find that the 10Be flux obtained from the travertines is comparable to the level produced by galactic cosmic rays and that travertines might have potential as a tool for investigating past cosmic-ray variations with annual resolution.

To explore the possibility of using ground ice archives for studies of the cosmogenic radionuclide 10Be, we analyzed the beryllium isotopes in ice wedges exposed in the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel and the Barrow Permafrost Tunnel in Alaska. We determined the concentrations of 10Be and 9Be in samples pretreated following two procedures: acidification before (procedure A) and after (procedure B) removal of particles. The 10Be and 9Be concentrations spanned wide ranges. Concentrations in procedure A samples were higher than those in procedure B samples. The 10Be/9Be ratios fell within a narrow range, and values from CRREL (about 8.5 × 10−9) and Barrow (about 7 × 10−9) were of the same order of magnitude. Further studies are needed to validate our findings and assess the feasibility of using the 10Be/9Be ratio of syngenetic ice wedges for reconstruction of 10Be variations due to cosmogenic and environmental changes, and radiometric dating of ice-wedge sequences that contain very old (beyond 1 Ma) ice.

Cosmogenic radionuclides have been widely used to decipher Earth surface processes. At the University of Tokyo Accelerator Mass Spectrometry facility (5 MV Tandem accelerator), we have been measuring both in-situ and meteoric cosmogenic 10Be and 26Al. In this paper, we report some development of methodology, including how to prepare target samples chemically to reduce their background. We then introduce some examples using the method to provide further insights into earth surface processes. These studies include: i) exposure dating to identify the growths and decays of the Antarctic ice sheet, ii) understanding ice shelf collapse history, iii) paleomagnetic excursion history reconstructions using ice cores, iv) understanding the erosion rates using depth profiles of mid latitude outcrops, v) identifying the timing of impact crater formation.

A 10Be analysis using only 10 μg of commercially available Be carrier was explored using Accelerator Mass Spectrometry (AMS) at the Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo. A combination of sample pretreatment and AMS analysis dedicated to this limited-carrier experiment enabled us to achieve reproducible measurements linear up to 10−14 (10Be/9Be ratio). Using this method we determined an order of 105 atoms g−1 10Be concentrations in sub-gram natural quartz samples taken from low (0.5–1 km) altitudes in Asian mid to high latitudes, and with apparent 10Be ages of 10–60 ka. Concentrations determined with the limited-carrier analysis were fairly consistent with those of previous ordinary analysis with tens of grams of quartz. Therefore, 10Be analysis using 10 μg of Be carrier was demonstrated for natural samples with an order of 105 atoms g−1, with an error of about 10%.

This paper reports the results of trial measurements of the concentration of cosmogenic 36Cl in an ice core recovered from Dome Fuji Station, Antarctica. Ten ice samples were extracted from depths corresponding to the Last Glacial Maximum and the early Holocene, with each sample comprising ∼150 g for a core length of 0.5 m (∼30–40 yr resolution). Analyses of 36Cl concentrations by accelerator mass spectrometry were successfully performed within ±10% precision, even for samples with low 36Cl/Cl values (∼3 × 10–14). The average 36Cl concentrations were 16 × 103 atoms g–1 for the Last Glacial Maximum, and 7 × 103 atoms g–1 for the early Holocene. The apparent 36Cl depositional flux at Dome Fuji Station during these periods was estimated to be approximately 2.5–3.5 × 104 atoms cm–2 yr–1.

We present preliminary data of our 10Be analysis of an ice core retrieved from Dome Fuji station, Eastern Antarctica for 1500–1810 yr AD. The concentration of 10Be from 1500-1810 yr AD ranged between 7.0 × 104 and 13.0 × 104 atoms g−1 and a prominent peak was observed in the period 1645–1715 yr AD (i.e., the Maunder Minimum period). An increase in the concentration was also observed in the periods before 1540 yr AD and near to 1800 yr AD. A comparison of our 10Be record with the South Pole 10Be record shows a clear similarity in their temporal fluctuations. On the other hand, our record shows ∼2.5 times higher concentration of 10Be than in the South Pole record attributable to the difference in local snow accumulation rates. These observations suggest a direct (uncomplicated) fallout of atmospheric 10Be onto inland Antarctica, which in turn, leads to a detailed 10Be stratigraphy throughout this region. We believe that the 10Be profiles of the ice cores from the Dome Fuji station are therefore likely to be a good proxy indicator of changes in solar activity.

Cosmogenic 10Be and 26Al dating of three erratic boulders in the southern coastal area of Lake Baikal was performed using accelerator mass spectrometry (AMS) at MALT (MicroAnalysis Laboratory, Tandem accelerator) of the University of Tokyo. We examined the accuracy of our 10Be AMS measurements and the differences in scaling factors for the 10Be and 26Al production rates. The measured 10Be and 26Al ages are 15–13 and 17–11.5 kyr, respectively. The 10Be ages suggest that release of the erratic boulders from a melting glacier occurred during the Bolling/Allerod warm period, when the land and lacustrine environments of the Baikal region changed dramatically.

MALT (Micro-Analysis Laboratory, Tandem accelerator) at The University of Tokyo is a research and service facility for elemental and isotopic analysis using a tandem accelerator for AMS, PIXE and NRA. Among these, AMS is the most promising technique at MALT. After the AMS-8 conference in 1999, the overall performance was greatly improved for 10Be-, 26Al- and 14C-AMS. For 10Be-AMS, the negative ion current was considerably increased by a new Cs-ionizer system and the replacement of the compound powder (Nb instead of Ag) for the BeO target. More than 3 μA current of BeO− ions can be extracted while it had been typically 1 μA before. For 26Al-AMS, by examining the sample ignition process, the negative ion gain was increased more than 200 nA (typically 100 nA before), which greatly improved the overall efficiency. For 14C-AMS, the 12C− current dependency problem has been moderated substantially by installing a fine controllable Cs oven and careful beam tuning. As a consequence, the precision is now better than 0.5% for modern carbon. In addition, systems for 36Cl-AMS and 129I-AMS are currently being developed for future research programs at MALT.

Sedimentary 10Be records covering the last 150 kyr were obtained from three cores collected at the Academician Ridge (BDP-96/hole2 core and VER96/st.3 core) and at the Buguldeika Saddle (BDP-93/hole2 core) in Lake Baikal. The 10Be concentrations of the three cores varied between 0.5×109 and 1.5×109 atoms/g, and coincidently dropped at the stratigraphic intervals of marine oxygen isotope stages (MIS) 2, 4, 5d and 6. The depositional fluxes of 10Be, on the other hand, generally rose in those stages having an increase in the dry bulk densities and sediment accumulation rates. These results are consistent with previous work (Horiuchi et al., 1999), suggesting that the dilution effects of low-10Be-concentration particles principally controlled the fluctuations of the 10Be concentrations of Lake Baikal sediments. Low-10Be-concentration particles have been intensively produced by mechanical weathering and physical erosion under the cold and dry climatic conditions during the peak glaciation period, and have been directly brought from the source areas into the lake as a result of the thin vegetative cover of the watershed.