Continuous 25-yr aerosol records at coastal Antarctica Part 2: variability of the radionuclides 7Be, 10Be and 210Pb

We investigated the variability of Pb-210, Be-7 and Be-10 in coastal Antarctic aerosol samples based on continuous, monthly and annually resolved time series obtained from Neumayer Station over the period 1983 to 2008. Clear seasonal cycles peaking in the local summer half year stand out as a common feature of all three radionuclide records. Time series analyses suggest that significant multiannual changes are confined to a 4-6 yr periodicity resembling that of the Southern Annual Mode index in case of Pb-210 and to the expected decadal solar cycle in case of the cosmogenic Be-isotopes. Both, changes in the meridional transport and surface inversion strength appear to drive the seasonal Pb-210 cycle, which generally peaks in November. In contrast, stratospheric air mass intrusions are proved to be the main reason for the Be-isotopes seasonality. This finding is revealed by enhanced Be-10/Be-7 ratios occurring during late summer / early autumn broadly concurrently with the individual Be-isotopes and the Be-7/Pb-210 ratio. The Be-10 and Be-7 records clearly reflect the decadal, solar-modulated production signal but, for unknown reasons, they substantially differ in their detailed pattern. It is ruled out, that an excess Be-7 production by solar energetic particles was responsible for this mismatch.