Summary
: We have conducted two hydrographic cruises crossing Deep Western Boundary Current (DWBC) of Antarctic Bottom Water (AABW) in Australia Antarctic Basin and measured chlorofluorocarbons (CFCs). Western region of the basin (around Kerguelen Plateau) has been occupied by R/V Mirai cruise in January 2004 and by RSV Aurora Australis cruise in January 2005. The cruise track is close to southern part of I08s transect of World Ocean Circulation Experiment (WOCE) Hydrographic Program (WHP). WHP I09 transect (along east of 115 degree E) has been revisited in December 2004 - January 2005 by RSV Aurora Australis cruise. We will show preliminary results of the CFCs measurements and compare them with previous data (http://whpo.ucsd.edu/). CFCs concentrations significantly increased in Antarctic Intermediate Water and AABW of I09 transect during recent decade. Highest CFCs concentrations in AABW were found in southern edge of the basin that would be core of Deep Western Boundary Current (DWBC). Assuming that the increases are caused by just temporal change in atmospheric CFCs mixing ratio (i.e. water circulating in steady state and the core water little mixing with surrounding water or mixing with no CFCs water), we estimate ventilation age of the water mass to be late 1990's. Ventilation age of DWBC around Kerguelen Plateau is also estimated to be end of 1980's - early 1990's. The AABW in the basin is thought to be formed in Adelie Coast and Ross Sea. The AABW would be spreading from the formation regions to western region of Australia Antarctic Basin within around 10 years by DWBC.