Dating a 109.9 m ice core from Dome A(East Antarctica) with volcanic records and a firn densification model

A 109.9 m ice core was extracted at a location about 300 m away from the Dome A summit(80°00′S,77°21″E) by the Chinese team of the International Trans-Antarctic Science Expedition(ITASE) during the 21st Chinese National Antarctica Research Expedition(CHINARE) in January 2005.Two independent methods were used for dating the ice core,volcanic event markers shown by prominent non-sea-salt sulfate(nss-SO42) and the Herron and Langway(H-L) firn densification model.Six promi-nent volcanic events(Agung 1963 AD,Tambora 1815 AD,Kuwae 1453 AD,Unknown 1259 AD,Taupo 186 AD and Pinatubo 1050 BC) were identified by comparison with other Antarctic ice cores.Based on the mean accumulation rates be-tween adjacent events,we estimate the age at the firn pore close-off depth(102 m) was 3516±100 a BP.This is the oldest close-off age ever reported from the Antarctic and the Greenland ice sheets.Calculations using the H-L model show that the age at the same depth is 3581±100 a BP.The two dating techniques differ by 65 years,or～1.8% of the record.We calculated the bottom age of the ice core as 4009±150 a BP using the volcanic dating method and 4115±150 a BP using the H-L model method.