Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai’i

Chemtob, S. M.; Rossman, George R.; Young, Edward; Ziegler, K.; Moynier, Frédéric; Eiler, John M.; Hurowitz, J. A.

doi:10.1016/j.gca.2015.07.026

Cited by 20 publications

(15 citation statements)

References 82 publications

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“…The anomalously low δ 30 DSi signal from glacial meltwaters requires either a light δ 30 DSi source or a heavy δ 30 DSi sink. The latter has only been documented with acidic hydrofluoric leaching of basalts 41 ; therefore, secondary phase dissolution or rapid leaching of the mineral surface is more likely the source. The glacial meltwaters are significantly undersaturated with respect to ASi (mean SI ASi = −2.1) 14 and have high pH (Fig.…”

Section: Discussionmentioning

confidence: 99%

The silicon cycle impacted by past ice sheets

et al. 2018

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Globally averaged riverine silicon (Si) concentrations and isotope composition (δ30Si) may be affected by the expansion and retreat of large ice sheets during glacial−interglacial cycles. Here we provide evidence of this based on the δ30Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ30Si measured in running waters (−0.25 ± 0.12‰), significantly lower than nonglacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06–0.17‰ of the observed ocean δ30Si rise (0.5–1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ30Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump.

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Section: Discussionmentioning

confidence: 99%

The silicon cycle impacted by past ice sheets

et al. 2018

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“…The heavier Si composition measured at LG could be an artefact of sampling bedrock with a weathering crust, rather than pristine samples. However, basalts have a lower isotopic composition (-0.3‰ to -0.2‰, Georg et al, 2007;Chemtob et al, 2015), so it is possible KS bedrock is isotopically lighter, as a result of basaltic intrusions. Nevertheless, we attribute variations in silicon isotope composition of SPM ASi to be largely a result of weathering processes at the glacier bed.…”

Section: Ks Andmentioning

confidence: 99%

“…5c, d). The offset could be the result of fractionation induced precipitation reactions, weathering of silicate rocks, comminution of particles, or a combination of all three (Andre et al, 2006;Chemtob et al, 2015). The suggesting it potentially forms as a result of aluminosilicate mineral weathering (Hellmann et al, 2012;Hawkings et al, 2017).…”

Section: Ks Andmentioning

confidence: 99%

“…Silicon isotopes (denoted by 30 Si) are increasingly used as a tool for studying continental weathering (Ding et al, 2004;Georg et al, 2007;Opfergelt et al, 2013;Chemtob et al, 2015), especially in riverine systems (Ding et al, 2004;Cardinal et al, 2010;Ding et al, 2011;Fontorbe et al, 2013;Frings et al, 2016). Silicon has three stable isotopes; 28 Si, 29 Si and 30 Si with relative abundances of 92.2%, 4.7% and 3.1% respectively (Ding et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

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Investigation of subglacial weathering under the Greenland Ice Sheet using silicon isotopes

Hatton

Hendry

Hawkings

et al. 2019

Geochimica et Cosmochimica Acta

100

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Subglacial chemical weathering plays a key role in global silicate weathering budgets, contributing to the cycling of silicon (Si) in terrestrial and marine systems and the potential drawdown of carbon dioxide from the atmosphere. Here, we use data from two Greenland Ice Sheet (GrIS) catchments to demonstrate how Si isotopes from dissolved and amorphous particulate fractions (δ 30 DSi and δ 30 ASi respectively) can be used together with major ion data to assess the degree of secondary silicate weathering product formation and redissolution in subglacial environments. We compare a time-series of summer melt seasons from the two study sites, which differ in catchment size (~600 km 2 for Leverett Glacier (LG) and ~36 km 2 for Kiattuut Sermiat (KS)). Subglacial waters from LG have elevated Na + and K + ions in relation to *Manuscript Ca 2+ and Mg 2+ ions, indicating a predominance of silicate weathering, whilst meltwaters from KS are characterised by carbonate weathering (hydrolysis and carbonation) throughout the melt season. Both catchments have mean δ 30 DSi values substantially lower than average riverine values (KS 0.41‰, LG-0.25‰, versus a global riverine mean of 1.25‰) and display a seasonal decline, which is more pronounced at LG. The δ 30 ASi values (discharge weighted mean values KS-0.44‰, LG-0.22‰) are lighter than the bedrock (mean values KS-0.18±0.12‰, LG 0.00±0.07‰) in both catchments, indicating a secondary weathering product origin or leaching of lighter isotopes during initial weathering of crushed rock. When used in combination, the major ion and silicon isotope data reveal that the extent of silicate weathering and secondary phase redissolution are more pronounced at LG compared to KS. Contrasting weathering regimes and subglacial hydrology between catchments need to be considered when estimating the δ 30 Si composition of silica exported into polar oceans from the GrIS, with larger catchments likely to produce fluxes of lighter δ 30 Si. As larger catchments dominate freshwater export to the ocean, GrIS meltwater is likely to be very light in isotopic composition, and the flux is likely to increase with ice melt as the climate warms.

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“…Although Si and Cr do have different physical and chemical properties, both elements share isotopic reservoir characteristics (Poitrasson, 2017;Qin and Wang, 2017) in terms of their limited isotopic variation within magmatic rocks and heavy average river and seawater isotopic compositions (Poitrasson, 2017;Savage et al, 2010;Savage et al, 2013;Scheiderich et al, 2015;Schoenberg et al, 2008). Further, the mobility, concentration, and isotopic composition of both elements in meteoric waters appear to respond to adsorption onto mineral surfaces and pore water Eh-pH conditions (Babechuk et al, 2017;Bern et al, 2010;Cardinal et al, 2010;Chemtob et al, 2015;D'Arcy et al, 2016;Delstanche et al, 2009;Farkaš et al, 2013;Frei et al, 2014;Opfergelt et al, 2009;Paulukat et al, 2015;Ziegler et al, 2005a;Ziegler et al, 2005b). The relative impact of each of these processes on Si and Cr isotopic signatures are likely to vary within different weathering regimes (e.g., desilication favoured under acidic conditions, and Cr being both acid soluble and redoxsensitive).…”

Section: Introductionmentioning

confidence: 99%

Silicon and chromium stable isotopic systematics during basalt weathering and lateritisation: A comparison of variably weathered basalt profiles in the Deccan Traps, India

et al. 2018

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Global biomass production is fundamentally affected by the hydrological cycling of elements at the Earth's surface. Continental weathering processes are the major source for most bioessential elements in marine environments and therefore affect primary productivity. In addition, critical zone biomass depends on energy and chemical exchange reactions in weathering profiles. The latter reservoirs are in turn influenced by different climatic conditions that control weathering and pore water parameters like pH and Eh, these then regulate mineral break down rates that dictate the mobility and mass flux of elements. Two Deccan Trap basalt-weathering profiles of contrasting age and alteration intensity provide a natural laboratory for investigating the effects of rock alteration on Si and Cr and their isotopic systematics. The sub-recent Chhindwara profile has progressed to a moderate degree of alteration (saprolite), whilst the Paleogene Bidar example displays an extremely altered laterite. The Chhindwara profile shows a near uniform Cr and Si concentration and isotopic composition, whereas the Bidar profile is characterised by an intense loss of Si, a large

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Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai’i

Cited by 20 publications

References 82 publications

The silicon cycle impacted by past ice sheets

The silicon cycle impacted by past ice sheets

Investigation of subglacial weathering under the Greenland Ice Sheet using silicon isotopes

Silicon and chromium stable isotopic systematics during basalt weathering and lateritisation: A comparison of variably weathered basalt profiles in the Deccan Traps, India

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