Stable silicon isotope signatures of marine pore waters – Biogenic opal dissolution versus authigenic clay mineral formation.

Ehlert, Claudia, Doering, Kristin, Wallmann, Klaus, Scholz, Florian, Sommer, Stefan, Grasse, Patricia, Geilert, Sonja and Frank, Martin (2016) Stable silicon isotope signatures of marine pore waters – Biogenic opal dissolution versus authigenic clay mineral formation. Geochimica et Cosmochimica Acta, 191 . pp. 102-117. DOI 10.1016/j.gca.2016.07.022.

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Abstract

Dissolved silicon isotope compositions have been analysed for the first time in pore waters (δ30SiPW) of three short sediment cores from the Peruvian margin upwelling region with distinctly different biogenic opal content in order to investigate silicon isotope fractionation behaviour during early diagenetic turnover of biogenic opal in marine sediments. The δ30SiPW varies between +1.1‰ and +1.9‰ with the highest values occurring in the uppermost part close to the sediment–water interface. These values are of the same order or higher than the δ30Si of the biogenic opal extracted from the same sediments (+0.3‰ to +1.2‰) and of the overlying bottom waters (+1.1‰ to +1.5‰). Together with dissolved silicic acid concentrations well below biogenic opal saturation, our collective observations are consistent with the formation of authigenic alumino-silicates from the dissolving biogenic opal. Using a numerical transport-reaction model we find that approximately 24% of the dissolving biogenic opal is re-precipitated in the sediments in the form of these authigenic phases at a relatively low precipitation rate of 56 μmol Si cm−2 yr−1. The fractionation factor between the precipitates and the pore waters is estimated at −2.0‰. Dissolved and solid cation concentrations further indicate that off Peru, where biogenic opal concentrations in the sediments are high, the availability of reactive terrigenous material is the limiting factor for the formation of authigenic alumino-silicate phases.

Document Type: Article
Additional Information: WOS:000384105300008
Keywords: Silicon isotopes; Pore water; Silicic acid; Biogenic opal; Authigenic alumino-silicates
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > SFB 754
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gca.2016.07.022
ISSN: 0016-7037
Projects: SFB754
Date Deposited: 11 Aug 2016 09:06
Last Modified: 11 Apr 2017 13:34
URI: http://oceanrep.geomar.de/id/eprint/33564

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