Beryllium-10 transport to Antarctica: Results from seasonally resolved observations and modeling

Cosmogenic Be-10 measured in polar ice cores has important application in the reconstruction of past solar activity. However, the processes controlling its atmospheric transport and deposition to the ice sheets are not fully understood. Here we use the seasonal changes in Be-10 concentrations in a 10 year monthly resolved ice core record from the Law Dome site (East Antarctica) in conjunction with ECHAM5-HAM general circulation model (GCM) simulations of Be-10 and Be-7 deposition as tools to examine this problem. Maximum Be-10 concentrations are observed in the ice core during the austral late summer to early autumn (summer-autumn), while minimum concentrations are observed during the austral winter. The GCM simulations, corroborated by earlier observations of Be-10:Be-7 ratios in Antarctica from the Georg von Neumayer air sampling station, suggest that the Be-10 concentration maximum is linked to direct input of stratospheric Be-10 from the Antarctic stratosphere to the lower levels of the Antarctic troposphere during the austral summer-autumn. This result contrasts with the modeled transport of Be-10 to Greenland, where the seasonal maximum in stratospheric input is seen in the late winter to spring, synchronous with the timing of the seasonal maximum in midlatitude stratosphere to troposphere exchange. Our results suggest that a different combination of processes is responsible for the transport of Be-10 to the Antarctic and Greenland ice sheets.