Measurement of 129I in ferromanganese crust with AMS

In the present study, the analytical method for 129iodine (129I) in ferromanganese crusts is developed and 129iodine/127iodine (129I/127I) ratio in ferromanganese crusts is measured by the accelerator mass spectrometry (AMS). The developed method is applied to analyze 129I/127I ratio in two ferromanganese crusts MP5D44 and CXD08-1 collected from the Mid-Pacific Ocean. The results show that 129I/127I ratio in MP5D44 and CXD08-1 crusts varies from 7×10–14 to 1.27×10–12, with the lowest value falling on the detection limit level of AMS reported by previous literatures. For the depth distribution of 129I/127I, it is found that both MP5D44 and CXD08-1 crusts have two growth generations, and the 129I/127I profiles in two generations all displayed an approximate exponential decay. According to the 129I/127I ratio, the generate age of bottom layer of MP5D44 and CXD08-1 was estimated to be 54.77 and 69.69 Ma, respectively.