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The competition between coastal trace metal fluxes and oceanic mixing from the 10 Be/ 9 Be ratio: Implications for sedimentary records
Author(s) -
Wittmann H.,
Blanckenburg F.,
Mohtadi M.,
Christl M.,
Bernhardt A.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl074259
Subject(s) - authigenic , overprinting , geology , seawater , sedimentary rock , oceanography , trace metal , terrigenous sediment , geochemistry , metal , chemistry , organic chemistry , metamorphic rock
At an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic 10 Be/ 9 Be 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 10 Be/ 9 Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10 Be/ 9 Be signatures. Together with increasing 10 Be/ 9 Be 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 10 Be/ 9 Be 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.