The competition between coastal trace metal fluxes and oceanic mixing from the 10Be/9Be ratio: Implications for sedimentary records. Issue 16 (19th August 2017)

• Record Type: Journal Article
• Authors: Wittmann, H.; von Blanckenburg, F.; Mohtadi, M.; Christl, M.; Bernhardt, A.
• Is Part Of: Geophysical research letters. Volume 44:Issue 16(2017)
• Page Start: 8443
• Page End: 8452
• Publication Date: 2017-08-19
• Subjects: meteoric 10Be/9Be ratio -- coastal trace metals -- oceanic mixing -- marine sedimentary records -- paleosediment fluxes -- boundary exchange; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL074259
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. Key Points: Meteoric 10 Be/ 9 Be in marine sediments shows terrestrial signals overprinted by seawater ratios 30 km offshore Chile coast (37°S) Net loss of reactive Fe and Be metals from pore water to sedimentary phase provides evidence for boundary exchange mechanism Implications for 10 Be/ 9 Be in marine records for paleodenudation flux reconstructions are that exchange with seawater cannot be neglected