26Al and 10Be in authigenic marine minerals

Abstract

We have used accelerator mass spectrometry to measure 26Al and 10Be in an oriented ferromanganese nodule from the North Pacific and, in phillipsites from a 100 cm long gravity core from the South Pacific Ocean. The growth rates of the nodule determined by measurements of the concentrations of 26Al and 10Be, and the 26Al/ 10Be ratios are (3.4 ± 1.0), (4.4 ± 1.4) and (2.8 ± 1.4) mm Ma −1, respectively. The extrapolated-to-surface atom ratio of 26Al/ 10Be in the nodule is (1.9 ± 1.0) × 10 −3. The sedimentation rates for the core determined by measurements of the concentrations of 26Al and 10Be and the 26Al/ 10Be ratios in the phillipsites are (0.12 ± 0.03), (0.23 ± 0.04) and (0.07 ± 0.03) mm ka~1, respectively. The extrapolated-to-surface value of the 26Al/ 10Be atom ratio in the phillipsites is (38 ± 16) × 10 −3. We conclude from the extrapolated-to-surface 26Al/ 10Be ratios, that 26Al and 10Be are not incorporated with equal efficiencies during the formation of these authigenic phases. However, the good agreement between the growth rates and sedimentation rates based on the separate measurements of 10Be and 26Al imply that the relative efficiencies of their incorporation have been constant through time in each phase.