10Be-dating of a manganese crust from Central North Pacific and implications for ocean palaeocirculation

Abstract

One of the most promising applications of the new 10Be detection technique using accelerator mass spectrometry is the determination of growth rates of Mn-nodules and crusts1–5. Because the half life of cosmogenic 10Be (1.5 Myr) is of the same order as the time needed for a few millimetres of nodule material to grow, 10Be is a useful tool for unravelling such evolution during the late Tertiary, when most nodules are assumed to have started their growth6. Mass spectrometric measurement of a 10Be profile across the manganese crust VA 13-2 from the Central Pacific, using a tandem van de Gr£ a ff accelerator, yields growth rates of 2.7 and 4.8 mm Myr−1 for the layers of the crust accumulated between Recent and 6 Myr BP and between 6 and 11 Myr, respectively. Using these measurements as well as 230Th dating, we have been able to distinguish boundaries between zones in the crust with different structures and chemical compositions and to assign ages to them. These ages are 0.12, 2.9–3.4, 5.7–6.7, 7–9, 10–12 and 13–16 Myr BP. All of these boundaries apparently coincide with the times reported for Quaternary and late Tertiary palaeoclimatic events, suggesting that the crust growth has been strongly influenced by palaeoclimate.