Rare Earth Element Signatures of Early Diagenesis in Pore Waters at Methane-Seeps from Hydrate Ridge, off Oregon
Abstract
Rare earth element (REE) concentrations of pore waters from Beggiatoa covered sediments at methane-seeps on southern Hydrate Ridge were analyzed using ion-exchange chromatography. Pore water REE concentration significantly increase within the first 2 cm below seafloor compared to bottom water concentration. Below 2 cm a gradual decrease is observed, reaching bottom water REE concentrations at 5 cm. At this depth, pore water sulfate is completely consumed and converted to hydrogen-sulfide through sulfate reduction. Shale-normalized REE patterns show a linear light REE-depletion across the REE series. At 2 cm a distinct convex-shaped, light REE-depleted pattern with a positive cerium (Ce) anomaly is observed. All other samples reveal negative Ce anomalies. These findings suggest (1) an active REE-source immediately below the sediment-water interface, which might be related to the anaerobic oxidation of methane coupled to sulfate reduction at this depth (c.f. Boetius et al., 2000. A marine consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623-626), and (2) REE-removal from pore waters probably caused by the uptake of REEs in authigenic minerals (e.g. carbonates, sulfides, barite).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B41D0325H
- Keywords:
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- 1050 GEOCHEMISTRY / Marine geochemistry