A global Ge isotope budget

Baronas, J. Jotautas, Hammond, Douglas E., McManus, James, Wheat, C. Geoffrey and Siebert, Christopher (2017) A global Ge isotope budget Geochimica et Cosmochimica Acta, 203 . pp. 265-283. DOI 10.1016/j.gca.2017.01.008.

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We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ74Ge composition of analyzed rivers ranges from 2.0 to 5.6‰, which is significantly heavier than previously determined values for silicate rocks (δ74Ge = 0.4–0.7‰, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ74Ge signatures suggests that the primary δ74Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150 °C) hydrothermal fluids analyzed in this study have δ74Ge of 0.7–1.6‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25–63 °C) hydrothermal fluids are heavier (δ74Ge between 2.9‰ and 4.1‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a δ74Gesw value of 3.2 ± 0.4‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation Δ74Gesolid-solution that is −0.6 ± 1.8‰.

Document Type: Article
Additional Information: WOS:000396795100015
Keywords: Ge/Si; Germanium; Hydrothermal fluids; Isotope fractionation; Seawater; Silicate weathering; Silicon; δ74Ge
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
DOI etc.: 10.1016/j.gca.2017.01.008
ISSN: 0016-7037
Date Deposited: 20 Feb 2017 10:01
Last Modified: 02 May 2017 09:55
URI: http://eprints.uni-kiel.de/id/eprint/36625

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