Impact of ambient conditions on the Si isotope fractionation in marine pore fluids during early diagenesis
Geilert, Sonja ; Grasse, Patricia ; Doering, Kristin LU
; Wallmann, Klaus
; Ehlert, Claudia
; Scholz, Florian
; Frank, Martin
; Schmidt, Mark
and Hensen, Christian
(2020)
In Biogeosciences
17(7).
p.1745-1763
- Abstract
Benthic fluxes of dissolved silicon (Si) from sediments into the water column are driven by the dissolution of biogenic silica (bSiO2) and terrigenous Si minerals and modulated by the precipitation of authigenic Si phases. Each of these processes has a specific effect on the isotopic composition of silicon dissolved in sediment pore fluids, such that the determination of pore fluid 30Si values can help to decipher the complex Si cycle in surface sediments. In this study, the 30Si signatures of pore fluids and bSiO2 in the Guaymas Basin (Gulf of California) were analyzed, which is characterized by high bSiO2 accumulation and hydrothermal activity. The 30Si signatures were investigated in the deep basin, in the vicinity of a hydrothermal... (More)
Benthic fluxes of dissolved silicon (Si) from sediments into the water column are driven by the dissolution of biogenic silica (bSiO2) and terrigenous Si minerals and modulated by the precipitation of authigenic Si phases. Each of these processes has a specific effect on the isotopic composition of silicon dissolved in sediment pore fluids, such that the determination of pore fluid 30Si values can help to decipher the complex Si cycle in surface sediments. In this study, the 30Si signatures of pore fluids and bSiO2 in the Guaymas Basin (Gulf of California) were analyzed, which is characterized by high bSiO2 accumulation and hydrothermal activity. The 30Si signatures were investigated in the deep basin, in the vicinity of a hydrothermal vent field, and at an anoxic site located within the pronounced oxygen minimum zone (OMZ). The pore fluid 30Sipf signatures differ significantly depending on the ambient conditions. Within the basin, 30Sipf is essentially uniform, averaging C1:2-0:1% (1 SD). Pore fluid 30Sipf values from within the OMZ are significantly lower (0:0-0:5 , 1 SD), while pore fluids close to the hydrothermal vent field are higher (C2:0-0:2 , 1SD). Reactive transport modeling results show that the 30Sipf is mainly controlled by silica dissolution (bSiO2 and terrigenous phases) and Si precipitation (authigenic aluminosilicates). Precipitation processes cause a shift to high pore fluid 30Sipf signatures, most pronounced at the hydrothermal site. Within the OMZ, however, additional dissolution of isotopically depleted Si minerals (e.g., clays) facilitated by high mass accumulation rates of terrigenous material (MARterr) is required to promote the low 30Sipf signatures, while precipitation of authigenic aluminosilicates seems to be hampered by high water = rock ratios. Guaymas OMZ 30Sipf values are markedly different from those of the Peruvian OMZ, the only other marine OMZ setting where Si isotopes have been investigated to constrain early diagenetic processes. These differences highlight the fact that 30Sipf signals in OMZs worldwide are not alike and each setting can result in a range of 30Sipf values as a function of the environmental conditions. We conclude that the benthic silicon cycle is more complex than previously thought and that additional Si isotope studies are needed to decipher the controls on Si turnover in marine sediment and the role of sediments in the marine silicon cycle.
(Less)
- author
- Geilert, Sonja
; Grasse, Patricia
; Doering, Kristin
LU
; Wallmann, Klaus
; Ehlert, Claudia
; Scholz, Florian
; Frank, Martin
; Schmidt, Mark
and Hensen, Christian
- publishing date
- 2020-04-03
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- silicon isotopes, pore fluids
- in
- Biogeosciences
- volume
- 17
- issue
- 7
- pages
- 19 pages
- publisher
- Copernicus GmbH
- external identifiers
-
- scopus:85083061205
- ISSN
- 1726-4170
- DOI
- 10.5194/bg-17-1745-2020
- language
- English
- LU publication?
- no
- additional info
- Funding Information: Acknowledgements. This work was part of the MAKS project funded by the German Ministry of Science and Education (BMBF). We appreciate the support of the master and crew of the R/V Sonne during the SO241 cruise. We thank Regina Surberg, Bet-tina Domeyer, and Anke Bleyer for analytical support during the cruise and on shore. Further thanks go to Tabitha Riff, Jutta Heinze, and Tyler Goepfert. Additional support for this work was provided by EU-COST Action ES1301 “FLOWS” (https://www.flows-cost. eu, last access: 30 March 2020) and the German Collaborative Research Centre (SFB) 754: Climate–Biogeochemistry Interactions in the Tropical Ocean, funded by the German Science Foundation. We would also like to thank an anonymous reviewer, Jill Sutton, and Damien Cardinal for their comments and constructive reviews. Publisher Copyright: © 2020 BMJ Publishing Group. All rights reserved.
- id
- 74da7985-2446-4799-8916-fb6a500e885e
- date added to LUP
- 2022-09-05 12:39:46
- date last changed
- 2022-09-15 21:27:51
@article{74da7985-2446-4799-8916-fb6a500e885e,
abstract = {{<p>Benthic fluxes of dissolved silicon (Si) from sediments into the water column are driven by the dissolution of biogenic silica (bSiO2) and terrigenous Si minerals and modulated by the precipitation of authigenic Si phases. Each of these processes has a specific effect on the isotopic composition of silicon dissolved in sediment pore fluids, such that the determination of pore fluid 30Si values can help to decipher the complex Si cycle in surface sediments. In this study, the 30Si signatures of pore fluids and bSiO2 in the Guaymas Basin (Gulf of California) were analyzed, which is characterized by high bSiO2 accumulation and hydrothermal activity. The 30Si signatures were investigated in the deep basin, in the vicinity of a hydrothermal vent field, and at an anoxic site located within the pronounced oxygen minimum zone (OMZ). The pore fluid 30Sipf signatures differ significantly depending on the ambient conditions. Within the basin, 30Sipf is essentially uniform, averaging C1:2-0:1% (1 SD). Pore fluid 30Sipf values from within the OMZ are significantly lower (0:0-0:5 , 1 SD), while pore fluids close to the hydrothermal vent field are higher (C2:0-0:2 , 1SD). Reactive transport modeling results show that the 30Sipf is mainly controlled by silica dissolution (bSiO2 and terrigenous phases) and Si precipitation (authigenic aluminosilicates). Precipitation processes cause a shift to high pore fluid 30Sipf signatures, most pronounced at the hydrothermal site. Within the OMZ, however, additional dissolution of isotopically depleted Si minerals (e.g., clays) facilitated by high mass accumulation rates of terrigenous material (MARterr) is required to promote the low 30Sipf signatures, while precipitation of authigenic aluminosilicates seems to be hampered by high water = rock ratios. Guaymas OMZ 30Sipf values are markedly different from those of the Peruvian OMZ, the only other marine OMZ setting where Si isotopes have been investigated to constrain early diagenetic processes. These differences highlight the fact that 30Sipf signals in OMZs worldwide are not alike and each setting can result in a range of 30Sipf values as a function of the environmental conditions. We conclude that the benthic silicon cycle is more complex than previously thought and that additional Si isotope studies are needed to decipher the controls on Si turnover in marine sediment and the role of sediments in the marine silicon cycle.</p>}},
author = {{Geilert, Sonja and Grasse, Patricia and Doering, Kristin and Wallmann, Klaus and Ehlert, Claudia and Scholz, Florian and Frank, Martin and Schmidt, Mark and Hensen, Christian}},
issn = {{1726-4170}},
keywords = {{silicon isotopes; pore fluids}},
language = {{eng}},
month = {{04}},
number = {{7}},
pages = {{1745--1763}},
publisher = {{Copernicus GmbH}},
series = {{Biogeosciences}},
title = {{Impact of ambient conditions on the Si isotope fractionation in marine pore fluids during early diagenesis}},
url = {{http://dx.doi.org/10.5194/bg-17-1745-2020}},
doi = {{10.5194/bg-17-1745-2020}},
volume = {{17}},
year = {{2020}},
}