Monday, 5 September 2005 - 10:30 AM

This presentation is part of: Ocean Sciences

Fluxes for cosmogenic Be isotopes across the ocean surface

Hisao Nagai1, Takeyasu Yamagata2, Chiharu Saito2, Takashi Saito1, and Hiroyuki Matsuzaki3. (1) Department of Chemistry, College of Humanities and Sciences, Nihon University, 3-25-40 Sakura-Josui, Setagaya-ku, Tokyo, 156-8550, Japan, (2) Graduate School of Integrated Basic Sciences, Nihon University, (3) Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo

The distribution of 7Be(53.35d) concentration in the atmosphere and ocean surface has been studied by many investigators, and is known to show characteristic latitudinal distribution [1,2]. On the other hand, there are a few studies for 10Be(1.5x106y) concentration in the atmosphere and ocean surface. We have already measured latitudinal distributions of 7Be and 10Be in the atmosphere over the Pacific Ocean and Antarctic Sea, and found similarity in these distributions and different 10Be/7Be values in the Northern and Southern Hemisphere [2]. In this study, we present results on distributions of 7Be and 10Be in ocean surface water and estimation of 7Be and 10Be fluxes across the ocean surface in the Pacific Ocean Applying a simple box model for the ocean surface layer, residence time of Be in surface water and 7Be and 10Be fluxes from atmosphere to ocean surface were estimated using the atomic ratio of Be isotopes in the atmosphere, (7Be /10Be=0.54), and ocean surface. Most of the estimated 7Be and 10Be fluxes were 0.01 to 0.02 and 0.03 to 0.04 atoms cm-2s-1, respectively, but in some region, fluxes were 3 times higher than the average value. The estimated fluxes include ambiguity derived from uncertainty in the average atomic ratio of Be isotopes in the atmosphere, since seasonal variation for the atomic ratio are not well known. The latitudinal distributions for 7Be and 10Be flux were similar to that of atmospheric concentrations, but slightly broader peak in the both Hemisphere. The distributions of 7Be and 10Be in surface water were also similar shape to those of atmospheric concentration and flux, but slightly different in the equator region where the 10Be concentrations were enriched. This was caused by the dissolved Be fraction with long residence time, and give overestimation in surface 10Be concentration supplied from the atmosphere, and underestimation in Be fluxes.

[1] J.A.Young and W.B.Silker, Earth and Planetary Science Letters, 50, 92-104 (1980) [2] H. Nagai, M. Uchida, M. Murayama, N. Ahagon, M. Ikehara, M. Imamura, S. Hatori and K. Kobayashi, abstract, 7th International Symposium on Accelerator Mass Spectrometry (1996.5, Tucson, U.S.A.)


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