10Be and 9Be concentrations in the deep sea sediments at Site 925, Ceara Rise, in the western equatorial Atlantic: implication of 10Be flux change

Abstract

The variations of 10 Be and 9 Be ßux over 7 Ma were studied at Site 925 on the Ceara Rise in the equatorial Atlantic. Agecorrected 10 Be ßuxes range from 50 to 270 ´ 10 7 atoms/cm 2 k.y. with an average value of over 100 ´ 10 7 atoms/cm 2 k.y. The relation of the age-corrected 10 Be ßux to the 9 Be ßux shows a positive correlation, suggesting the 10 Be is associated with the terrigenous fractions. However, despite the fact that the concentration of 10 Be derived from the Amazon drainage area should be expected to be much lower than that in the marine sediments, the ßuxes of 10 Be show high values. This result indicates that the 10 Be in the ocean was scavenged by suspended materials like Þne-grained clays in the process of transportation from the Amazon drainage area. The variations of both Be ßuxes over the last 7 Ma in this area may result from local or regional change in the inputs of Amazon-derived terrigenous sediments.