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A First Look at Dissolved Ge Isotopes in Marine Sediments

Baronas, J. Jotautas and Hammond, Douglas E. and Rouxel, Olivier J. and Monteverde, Danielle R. (2019) A First Look at Dissolved Ge Isotopes in Marine Sediments. Frontiers in Earth Science, 7 . Art. No. 162. ISSN 2296-6463. doi:10.3389/feart.2019.00162.

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The removal of chemical species from seawater during the precipitation of authigenic minerals is difficult to constrain but may play a major role in the global biogeochemical cycles of some elements, including silicon (Si) and germanium (Ge). Here, we present Ge/Si, δ^(74)Ge, and supporting chemical data of pore waters and core incubations at three continental margin sites in California and the Gulf of Mexico. We used these data to partition Ge release and uptake by the various allogenic (delivered via sedimentation) and authigenic (formed in situ) phases in these sediments. About half of the pore water Ge (δ^(74)Ge_(pw) = 1.3–2.4‰) is supplied by biogenic silica dissolution (δ^(74)Ge ~ 3‰), with the other half contributed by lithogenic particulates (δ^(74)Ge ~ 0.6‰). The highest Ge/Si (~3μmol/mol) and lowest δ^(74)Ge (1.3–1.9‰) are observed at the Fe redox horizon, suggesting a supply from detrital Ge-rich Fe oxides. The precipitation of authigenic phases (most likely aluminosilicate clays) in deeper sediments preferentially incorporates Ge over Si, resulting in low pore water Ge/Si (~0.3μmol/mol). The lack of corresponding δ^(74)Ge_(pw) trend indicates negligible Ge isotope fractionation during this process. Ge fluxes measured via core incubations were variable and appeared strongly controlled by Fe redox behavior near the sediment-water interface. In some cases, reductive Fe oxide dissolution appeared to enhance the benthic Ge flux by over 100% and released fractionated low δ74Ge of ~−0.7‰, resulting in overall benthic δ^(74)Ge_(inc) between –0.2 and 3.6‰, depending on Fe oxide contribution to Ge flux. We estimate that detrital inputs supply 12–31% of total dissolved Ge to continental margin pore fluids globally, resulting in an average pore water and benthic flux δ^(74)Ge between 2.2 and 2.7‰. Assuming 10-60% of pore water Ge is captured by the authigenic aluminosilicate sink, the dissolved Ge flux to the ocean derived from terrigenous inputs should be roughly 2.5–6.6 Mmol/y, much higher than previously estimated. Our results imply that authigenic Si burial in continental margins should be in the range of 1–8 Tmol/y (best estimate 3.1 Tmol/y), sufficient to close the global marine Si budget.

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URLURL TypeDescription
Baronas, J. Jotautas0000-0002-4027-3965
Rouxel, Olivier J.0000-0002-1431-222X
Monteverde, Danielle R.0000-0002-0198-8220
Additional Information:© 2019 Baronas, Hammond, Rouxel and Monteverde. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Received: 14 April 2019; Accepted: 06 June 2019; Published: 21 June 2019. Data Availability: All data discussed in this study is supplied in the main text and Supplementary Tables. Author Contributions: JB and DH designed the study. JB and DM collected the samples. JB and OR performed Ge isotope analyses. JB performed the experiments and modeling and wrote the article, with input from all co-authors. Financial support for the SPB cruise was provided by US National Science Foundation (NSF) grant OCE-1260692 to DH. SMB cruise was supported by US NSF grants OCE-0962209 to Sergio Sañudo-Wilhelmy, OCE-0934073 to Douglas Capone, and PLR-1029878 to William Berelson. Additional support was provided by US NSF grant OCE-1061700 to DH. JB was also supported by a CUAHSI Pathfinder graduate student fellowship, an InterRidge research fellowship, and a John Montagne Award from GSA Quaternary Geology and Geomorphology Division. Support for OR was provided by the Institut Carnot Ifremer EDROME and the LabexMer ANR-10-LABX-19-01. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We thank the crew of R/V Yellowfin, Nick Rollins, Elias Karkabi, Brian Seegers, and Will Berelson for their assistance with sample collection and processing. We also thank Emmanuel Ponzevera for assistance with Ge isotope measurements at Ifremer. Two reviewers are thanked for their constructive comments that helped improve the manuscript.
Funding AgencyGrant Number
Consortium of Universities for the Advancement of Hydrologic Science (CUAHSI)UNSPECIFIED
InterRidge Research FellowshipUNSPECIFIED
Geological Society of AmericaUNSPECIFIED
Institut Carnot Ifremer EDROMEUNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-10-LABX-19-01
Record Number:CaltechAUTHORS:20190711-103025973
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Official Citation:Baronas JJ, Hammond DE, Rouxel OJ and Monteverde DR (2019) A First Look at Dissolved Ge Isotopes in Marine Sediments. Front. Earth Sci. 7:162. doi: 10.3389/feart.2019.00162
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97054
Deposited By: Tony Diaz
Deposited On:11 Jul 2019 23:13
Last Modified:16 Nov 2021 17:25

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