Be isotopes in rivers/estuaries and their oceanic budgets

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10Be and 9Be have been determined in several North American rivers and in the estuaries of San Francisco Bay and the Pearl River (China). The average fluvial concentration of dissolved 10Be in the rivers is 3220 ± 1960 (1σ) atoms/g, almost an order of magnitude higher than the observed estuarine values and slightly higher than the 10Be concentration in the ocean ( ∼ 1700 atoms/g). For dissolved 9Be, a similar order-of-magnitude drop in concentration also occurs in going from rivers (750 ± 740 pM) to estuaries (80–140 p M). However, in contrast to the 10Be situation, there appears another order-of-magnitude drop from estuaries to the ocean, which has 9Be concentrations of 5–30 p M. In spite of the wide range of concentrations for both isotopes in river and estuarine waters, 10Be/ 9Be ratios range mostly from 2 to 12 × 10 −9, with a median value of 7 × 10 −9 (atom/atom), and are much lower than the seawater ratio of ∼ 10 −7. In the rivers studied, a given volume of water contains roughly equal amounts of particulate and dissolved 10Be. The 10Be concentration in particulate matter ranges from 2 × 10 6 to 1 × 10 9 atoms/g-particulate with a median value of about 5 × 10 7 atoms/g-particulate. A two-box model calculation shows that coastal regions play an important role in the removal of Be isotopes from the ocean and that eolian dusts may be the chief source of oceanic 9Be. Because of the marginal removal effect, the overall oceanic residence time of Be should be shorter than the residence time of 500–1200 yr estimated for the open ocean.