<sup>10</sup>Be/<sup>9</sup>Be Ratios Reveal Marine Authigenic Clay Formation
Anne Bernhardt, Marcus Oelze, Julien Bouchez, Friedhelm von Blanckenburg, Mahyar Mohtadi, Marcus Christl, Hella Wittmann
Abstract
Abstract As reverse weathering has been shown to impact long‐term changes in atmospheric CO 2 levels, it is crucial to develop quantitative tools to reconstruct marine authigenic clay formation. We explored the potential of the beryllium (Be) isotope ratio ( 10 Be/ 9 Be) recorded in marine clay‐sized sediment to track neoformation of authigenic clays. The power of such proxy relies on the orders‐of‐magnitude difference in 10 Be/ 9 Be ratios between continental Be and Be dissolved in seawater. On marine sediments collected along a Chilean margin transect we chemically extracted reactive phases and separated the clay‐sized fraction to compare the riverine and marine 10 Be/ 9 Be ratio of this fraction. 10 Be/ 9 Be ratios increase fourfold from riverine to marine sediment. We attribute this increase to the incorporation of Be high in 10 Be/ 9 Be from dissolved biogenic opal, which also serves as a Si‐source for the precipitation of marine authigenic clays. 10 Be/ 9 Be ratios thus sensitively track reverse‐weathering reactions forming marine authigenic clays.