Volcanic and solar activity, and atmospheric circulation influences on cosmogenic 10Be fallout at Vostok and Concordia (Antarctica) over the last 60 years

The cosmogenic nuclide beryllium-10 (Be-10), recovered from ice cores, is often used to study solar activity on long time-scales. However, the Be-10 signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the Be-10 signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60 years were studied at a sub-annual resolution. Three factors that contribute to the Be-10 signal were identified. First, a significant period of approximately 11 yr that can be associated with the modulation of Be-10 production by solar activity was detected in both records. The solar imprint constitutes 20-35% of the variance within the total signal. The 11-yr Be-10 snow component was attenuated by a factor of similar to 0.5 and was delayed by similar to 1.4 yr compared to the Be-10 production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric Be-10 reservoir with an 11-yr modulation that was attenuated and delayed (with respect to Be-10 polar production) and to a tropospheric Be-10 reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in Be-10 concentrations that were similar to 66% and similar to 35% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published Be-10 ice core records could be reinterpreted because spikes in Be-10 concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact Be-10 transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of similar to 4 yr was determined in both Be-10 records, corresponding to similar to 26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean-atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate. (C) 2011 Elsevier Ltd. All rights reserved.