The variations of 10Be and 9Be flux over 7 Ma were studied at Site 925 on the Ceara Rise in the equatorial Atlantic. Age-corrected 10Be fluxes range from 50 to 270 X 107 atoms/cm2 k.y. withan average value of over 100 X 107 atoms/cm2 k.y. The relation of the age-corrected 10Be flux to the 9Be flux shows a positive correlation, suggesting the 10Be is associated with the terrigenous fractions. However, despite the fact that the concentration of 10Be derived from the Amazon drainage area should be expected to be much lower than that in the marine sediments, the fluxes of 10Be show high values. This result indicates that the 10Be in the ocean was scavenged by suspended materials like fine-grained clays in the process of transportation from the Amazon drainage area. The variations of both Be fluxes over the last 7 Ma in this area may result from local or regional change in the inputs of Amazon-derived terrigenous sediments.
1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060, Japan. murayama@ees.hokudai.ac.jp
3Department of Chemistry, College of Humanities and Science, Nihon University, Tokyo 156, Japan.
4Institute for Nuclear Study, University of Tokyo, Tokyo 188, Japan.
5Micro Analysis Laboratory, Tandem Accelerator Research Center for Nuclear Science and Technology, University of Tokyo, Tokyo 113, Japan.
6Ocean Research Institute, University of Tokyo, Tokyo 164, Japan.
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