¹⁰Be Dating of large manganese nodules from world oceans

Abstract

The results of ¹⁰Be and ⁹Be measurements in several sections of ten large manganese nodules are presented along with U and Th isotope data on five of them. The ¹⁰Be and ¹⁰Be/⁹Be methods yield growth rates (covering a period of 5-10 Ma) which are in excellent agreement with each other. In three cases, these rates are also in very good agreement with those derived from the ²³⁰Th methods, whereas in the other two the ²³⁰Th-based rates are faster by over a factor of two. Based on the discrepancy between the inventory of ¹⁰Be (as well as ²³⁰Th) in nodules and the overhead seawater column, it is calculated that the former scavenge their Be and Th isotopes from 2-900 m of the overhead water column. The deduced 9Be concentrations of ocean water based on its ¹⁰Be contents and the ¹⁰Be/⁹Be ratios of nodule surfaces are found to be in good agreement with the direct ⁹Be measurements of seawater implying that ⁹Be in nodules (like ¹⁰Be) is mostly authigenic.