Using Stable Isotopes to Disentangle Marine Sedimentary Signals in Reactive Silicon Pools

Pickering, Rebecca A.; Cassarino, Lucie; Hendry, Katharine R.; Wang, Xiangli L.; Maiti, Kanchan; Krause, Jeffrey W.

doi:10.1029/2020gl087877

Cited by 23 publications

(34 citation statements)

References 86 publications

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“…The composition of the 0.1 M HCl leach (Si-HCl pool) was very isotopically light, averaging -2.88 ±0.17‰ (n=20), almost identical to the mean value analysed in the same leach phase of Mississippi River plume sediments (-2.89 ±0.45‰) (Pickering et al, 2020). These values were within long term reproducibility and so indistinguishable across the stations.…”

Section: Isotopic Composition Of the Operational Poolsmentioning

confidence: 50%

“…Operationally defined reactive pools of Si were extracted from the solid phase following Pickering et al (2020). An additional study was also carried out here to assess the influence of oven drying and grinding sediment samples prior to isotopic analysis (see supp.…”

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

“…2). This sequential digestion procedure separates Si into operational pools based on the conditions, kinetics (time dependent) and sequence of the reaction (Pickering et al, 2020;Rahman et al, 2016;Michalopoulos and Aller, 2004;DeMaster, 1981). Reagents were added to 50-70 mg of thawed (dry weight) or dried sediment in the following sequence: 36 mL 0.1 M HCl (in-house distilled) for 18 hours (Si-HCl pool); 25 mL 0.1 M Na 2 CO 3 (Sigma-Aldrich BioXtra) for 5 hours in an 85 o C water bath (Si-Alk pool); 10 mL 4 M NaOH (Honeywell Fluka Trace SELECT) for 2 hours at 85 o C (Si-NaOH pool).…”

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

“…Reagents were added to 50-70 mg of thawed (dry weight) or dried sediment in the following sequence: 36 mL 0.1 M HCl (in-house distilled) for 18 hours (Si-HCl pool); 25 mL 0.1 M Na 2 CO 3 (Sigma-Aldrich BioXtra) for 5 hours in an 85 o C water bath (Si-Alk pool); 10 mL 4 M NaOH (Honeywell Fluka Trace SELECT) for 2 hours at 85 o C (Si-NaOH pool). Predominantly, these sequential extractions are thought to remove authigenic metal oxide coatings, BSi and LSi phases respectively (Michalopoulos and Aller, 2004;Pickering et al, 2020). In addition to the digestion sequence applied by Pickering et al (2020), here 5 mL of 10% H 2 O 2 (Fisher Chemical Extra Pure SLR) was added to the sediment samples for 30 minutes after the 0.1 M HCl leach to remove diluting organic phases (Mortlock and Froelich, 1989).…”

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

“…Predominantly, these sequential extractions are thought to remove authigenic metal oxide coatings, BSi and LSi phases respectively (Michalopoulos and Aller, 2004;Pickering et al, 2020). In addition to the digestion sequence applied by Pickering et al (2020), here 5 mL of 10% H 2 O 2 (Fisher Chemical Extra Pure SLR) was added to the sediment samples for 30 minutes after the 0.1 M HCl leach to remove diluting organic phases (Mortlock and Froelich, 1989). After each digestion, supernatants were extracted after centrifugation and the residual sediment was rinsed in triplicate with Milli-Q water (18.2 MΩ) to remove any remaining reagent.…”

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

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Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

Ward¹,

Hendry²,

Arndt³

et al. 2022

Preprint

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Biogeochemical cycling of silicon (Si) in the Barents Sea is under considerable pressure from physical and chemical changes, including dramatic warming and sea ice retreat, together with a decline in dissolved silicic acid (DSi) concentrations of Atlantic inflow waters since 1990. Moreover, further expansion of the Atlantic realm (termed `Atlantification') is expected to shift phytoplankton community compositions away from diatom-dominated spring bloomsin favour of Atlantic flagellate species (coccolithophore-dominated). The changes in pelagic primary production will alter the composition of the material comprising the depositional flux, which will subsequently in influence the recycling processes at and within the seafloor. In this study we assess the predominant controls on the early diagenetic cycling of Si, a key nutrient in marine ecosystems, by combining stable isotopic analysis of pore water DSi and of operationally defined reactive pools of the solid phase. We show that low biogenic silica (BSi) contents (0.39-0.52 wt% or 92-185 μmol g dry wt-1) drive correspondingly low asymptotic concentrations of pore water DSi (~100 μM). However, while these surface sediments appear almost devoid of BSi, we present evidence for the rapid recycling of bloom derived BSi that generates striking transient peaks in sediment pore water [DSi], which is a feature that is subject to future shifts in phytoplankton community compositions. Using a simple mass balance calculation we show that the pore water DSi pool is supplemented by a lithogenic Si source (LSi), while our sediment pore water Si isotopic profiles also uncover a coupling of the iron (Fe) and Si cycles. This has previously been observed in lower latitude marine sediment systems and thus provides further support for a redox influence on oceanic pore water DSi. We suggest that a high LSi:BSi ratio and apparent Fe (oxyhydr)oxide influence could lead to a degree of stability in the annual background benthic flux of DSi despite the pressures on pelagic phytoplankton communities. Coupled with supporting isotopic evidence for the precipitation of authigenic clays in Barents Sea sediment cores, our observations have implications for the sink vs recycling terms in the regional Si budget.

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Section: Isotopic Composition Of the Operational Poolsmentioning

confidence: 50%

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

Section: Solid Phase Extraction and Dsi Concentration Analysismentioning

confidence: 99%

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Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

Ward¹,

Hendry²,

Arndt³

et al. 2022

Preprint

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Benthic diatoms modify riverine silicon export to a marine zone in a hypertidal estuarine environment

et al. 2022

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Riverine dissolved silicon (DSi) and biogenic silica (BSi) are modulated along the estuarine gradient by several biotic and abiotic processes governed by physical forcings. An important area controlling silicon transport in alluvial estuaries with large intertidal mudflats is the benthic diatom-dominated biofilm system. Here, the hypertidal Severn Estuary, UK, has been used as a case study to improve our understanding of silicon transport in these benthic-dominated systems. We present the first time-series dataset of Si concentrations in the Severn. River and tidal hydrodynamics drove spatio-temporal changes in DSi. The longitudinal profile of DSi followed the classical view of dilution with downstream transport. Despite low riverine supply of BSi and low siliceous-phytoplankton production, relatively high BSi concentrations were measured in the Severn Estuary (maximum of 14.9 mg/L), which accounted for over 70% of the total bioavailable silicon present and were characterised by isotopically heavy waters (δ30Si of + 0.9 to + 1.1‰). Benthic biofilms (microphytobenthos) on the intertidal mudflats contained significant biomass (measured as chlorophyll a concentration with a maximum of 116.8 ± 16.2 µg/g dw. sed) with high productivity, driven by their photoprotective adaptions to these harsh intertidal environments, contributing to isotopically heavy mudflat water (δ30Si of + 1.19 to + 2.03‰), and resulting in high benthic BSi content in the spring (0.74 ± 0.03%) and summer (0.76 ± 0.05%). The fast-flowing tidal currents resulted in high bottom shear stress which likely exceeded the erosion thresholds of the biofilms, transporting the sediment-BSi matrix into the water column. Suspended particulate matter (SPM) and BSi remained tightly coupled in the estuarine water column (bioflocculation), and experienced the series of erosion–deposition events, burial/dissolution and export out of the estuary. Our novel observations improve understanding of the complex processes governing Si transport in hypertidal, benthic-dominated estuaries, and highlights the importance of tightly coupled benthic-pelagic systems in influencing the terrestrial silicon export to a marine zone.

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Application of sequential alkaline amorphous silica extraction for Cenozoic and early Paleozoic rocks

et al. 2023

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Using Stable Isotopes to Disentangle Marine Sedimentary Signals in Reactive Silicon Pools

Cited by 23 publications

References 86 publications

Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

Benthic diatoms modify riverine silicon export to a marine zone in a hypertidal estuarine environment

Application of sequential alkaline amorphous silica extraction for Cenozoic and early Paleozoic rocks

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