The half life of32Si determined from a varved Gulf of California sediment core

Excess²¹⁰Pb measurements and varve chronology were used to establish a sediment accumulation rate of 0.19 cm/yr in a 95-cm-long box core raised from the Gulf of California. Varve thickness is unchanged over the entire length of the core, indicating a constant rate of sediment accumulation. The³²Si specific activity of biogenic silica shows an exponential decrease with depth in this core. The half life of³²Si, calculated from these data and the 0.19-cm/yr sediment accumulation rate, is276 ± 32 years. As most of the silica and³²Si supplied to the Gulf of California is a result of upwelling of deep ocean water, this half life determination should be relatively insensitive to secular variations in the atmospheric supply of³²Si.