River fluxes to the sea from the ocean始s ¹⁰Be/⁹Be ratio

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• 作者：Friedhelm von Blanckenburg ; Julien Bouchez
• 关键词：seawater chemistry ; cosmogenic isotopes ; weathering ; erosion ; river flux
• 刊名：Earth and Planetary Science Letters
• 出版年：1 February, 2014
• 年：2014
• 卷：387
• 期：Complete
• 页码：34-43
• 全文大小：1014 K

文摘

The ratio of the meteoric cosmogenic radionuclide ¹⁰Be to the stable isotope ⁹Be is proposed here to be a flux proxy of terrigenous input into the oceans. The ocean始s dissolved ¹⁰Be/⁹Be is set by (1) the flux of meteoric ¹⁰Be produced in the atmosphere; (2) the denudational flux of the rivers discharging into a given ocean basin; (3) the fraction of ⁹Be that is released from primary minerals during weathering (meaning the ⁹Be transported by rivers in either the dissolved form or adsorbed onto sedimentary particles and incorporated into secondary oxides); and (4) the fraction of riverine ¹⁰Be and ⁹Be actually released into seawater. Using published ¹⁰Be/⁹Be data of rivers for which independent denudation rate estimates exist we first find that the global average fraction of ⁹Be released during weathering into river waters and their particulate load is 20% and does not depend on denudation rate. We then evaluate this quantitative proxy for terrigenous inputs by using published dissolved seawater Be isotope data and a compilation of global river loads. We find that the measured global average oceanic dissolved ¹⁰Be/⁹Be ratio of about is satisfied by the mass balance if only about 6% of the dissolved and adsorbed riverine Be is eventually released to the open ocean after escaping the coastal zone. When we establish this mass balance for individual ocean basins good agreement results between ¹⁰Be/⁹Be ratios predicted from known river basin denudation rates and measured ocean ¹⁰Be/⁹Be ratios. Only in the South Atlantic and the South Pacific the ¹⁰Be/⁹Be ratio is dominated by advected Be and in these basins the ratio is a proxy for ocean circulation. As the seawater ¹⁰Be/⁹Be ratio is faithfully recorded in marine chemical precipitates the ¹⁰Be/⁹Be ratio extracted from authigenic sediments can now serve to estimate relative changes in terrigenous input into the oceans back through time on a global and on an ocean basin scale.