Abstract
AbstractAt an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic 10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the marine authigenic phase in surface sediments along a coast‐perpendicular transect and compared to samples from their riverine source. We find evidence for growth of authigenic rims through coprecipitation, not via reversible adsorption, that incorporate an open ocean 10Be/9Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10Be/9Be signatures. Together with increasing 10Be/9Be ratios, particulate‐bound Fe concentrations increase, which we attribute to release of Fe‐rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleodenudation flux reconstructions are the following: in coast‐proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater, whereas sites beneath well‐mixed seawater will preserve global flux signatures.
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