Thorium isotopes measurements inside internal layers of manganese deposits from the South Pacific Ocean

The ratio of 230 Thorium excess over 232 Thorium isotopes has been determined for different layered deposit zones inside ferromanganese nodules and crusts retrieved in the South Pacific Ocean during various R/V Eltanin cruises. Samples were prepared from the nodules and crusts by peeling or scraping successive layers and measuring the resultant decrease in thickness with calipers. The samples were then ground to a fine powder and split into two aliquots, one for U and Th isotopic analysis, the other for elemental analysis. The Thorium was extracted using Thenoyltrifluoroacetone (TTA) and measured using Alpha-particle spectroscopy.