Decadal Changes of Bomb Radiocarbon in the Subtropical South Pacific Ocean Between 1992 and 2003

Abstract

A basin-scale repeat hydrography of the WOCE-P06 line along approximately 32°S has revealed decadal changes of bomb-produced radiocarbon in the subtropical South Pacific Ocean between 1992 and 2003. Surface δ14C decreased by about 30%. A δ14C decrease was also found in the upper thermocline from the surface to 400 m water depth. In the lower thermocline, from 400 m to 1100 m depth, however, δ14C increased, with a maximum increase of 25% at 700 m depth. This contrast between the upper and lower thermoclines resulted in an overall 10% increase of the specific column inventory of bomb 14C from 1992 to 2003. The global ocean inventory of bomb 14C was assessed based on the specific inventory increase in the subtropical South Pacific Ocean. The meridional distribution of bomb 14C in the early 1990s suggests that the bomb 14C increases observed along 32°S in 2003 were primarily caused by mixing along isopycnals.