²⁶Al-¹⁰Be systematics in deep-sea sediments

We report the development of a NaOH-leaching technique to extract the authigenic Al and Be in marine sediments, which should allow the sedimentary signals of cosmogenic ²⁶Al and ¹⁰Be to be more effectively studied as geochemical/geophysical tracers. The technique has been applied to the study of ²⁶Al and ¹⁰Be in opal-rich sediments from the North Pacific. The ²⁶Al/²⁷Al and ¹⁰Be/⁹Be ratios of ∼3 × 10^-14 and 1 × 10^-7 leached from the sediments are higher than those in the total sediments by factors of 3-10 and 2-3, respectively. The authigenic ¹⁰Be/⁹Be ratios are similar to those in deep waters at the study site, pointing to the potential usefulness of the ratios in paleoceanographic studies. The fractions of total Be and Al in the sediment studied that are of authigenic origin average about 40 and 17%, respectively. Estimated ²⁶Al/²⁷Al ratios in detrital sediments are ≤ 10^-15, low enough to indicate that the source of ²⁶Al in the ocean mainly comes from atmospheric production. In the study area, the deposition flux of ²⁶Al is comparable to its atmospheric supply. However, the deposition flux of ¹⁰Be is about threefold higher than the atmospheric input, signifying lateral transport of ¹⁰Be from the open ocean to this area of relatively high particle flux. The ²⁶Al/¹⁰Be ratio, being insensitive to the oceanic influx of lithogenic particles, may serve as a valuable proxy for paleoproductivity. Both the authigenic and total-sediment ²⁶Al/²⁷Al and ¹⁰Be/ ⁹Be ratios decreased significantly at ∼6 ka, which could reflect an enhanced input of windblown lithogenic particles to the North Pacific. While the enhanced dust input did not significantly alter the deep-water ⁹Be concentration, it contributed to the observed increase of authigenic ⁹Be flux to the sediment.