Weathering Dynamics Under Contrasting Greenland Ice Sheet Catchments

Urra, Alexandra; Wadham, Jemma L.; Hawkings, Jon R.; Telling, Jon; Hatton, Jade E.; Yde, Jacob C.; Hasholt, Bent; As, Dirk van; Bhatia, Maya P.; Nienow, Peter

doi:10.3389/feart.2019.00299

Cited by 19 publications

(24 citation statements)

References 77 publications

(155 reference statements)

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“…Despite the cold and dry conditions in the Dry Valleys, analysis of stream hyporheic zones has shown primary silicate weathering rates to be comparable to temperate environments (Gooseff et al, 2002). This concurs with other studies challenging the assumption that high latitude systems have lower weathering rates (Huh et al, 1998;Wadham et al, 2010;Urra et al, 2019).…”

Section: Introductionsupporting

confidence: 87%

Silicon Isotopic Composition of Dry and Wet-Based Glaciers in Antarctica

et al. 2020

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Glaciers and ice sheets export significant amounts of silicon (Si) to downstream ecosystems, impacting local and potentially global biogeochemical cycles. Recent studies have shown Si in Arctic glacial meltwaters to have an isotopically distinct signature when compared to non-glacial rivers. This is likely linked to subglacial weathering processes and mechanochemical reactions. However, there are currently no silicon isotope (δ 30 Si) data available from meltwater streams in Antarctica, limiting the current inferences on global glacial silicon isotopic composition and its drivers. To address this gap, we present dissolved silicon (DSi), δ 30 Si DSi , and major ion data from meltwater streams draining a polythermal glacier in the region of the West Antarctic Peninsula (WAP; King George Island) and a cold-based glacier in East Antarctica [Commonwealth Stream, McMurdo Dry Valleys (MDV)]. These data, alongside other global datasets, improve our understanding of how contrasting glacier thermal regime can impact upon Si cycling and therefore the δ 30 Si DSi composition. We find a similar δ 30 Si DSi composition between the two sites, with the streams on King George Island varying between-0.23 and +1.23 and the Commonwealth stream varying from-0.40 to +1.14. However, meltwater streams in King George Island have higher DSi concentrations, and the two glacial systems exhibit opposite DSi-δ 30 Si DSi trends. These contrasts likely result from differences in weathering processes, specifically the role of subglacial processes (King George Island) and, supraglacial processes followed by in-stream weathering in hyporheic zones (Commonwealth Stream). These findings are important when considering likely changes in nutrient fluxes from Antarctic glaciers under climatic warming scenarios and consequent shifts in glacial thermal regimes.

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Section: Introductionsupporting

confidence: 87%

Silicon Isotopic Composition of Dry and Wet-Based Glaciers in Antarctica

et al. 2020

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“…In contrast to the major cations, we observed substantial depletion of dissolved Si and Fe in the field samples ( Figures 4A,D), consistent with the subglacial precipitation of aSi (Hawkings et al, 2017;Hatton et al, 2019a;Urra et al, 2019) and Fe oxyhydroxide phases (Wimpenny et al, 2010;Hindshaw et al, 2014;Aciego et al, 2015;Stevenson et al, 2017;Auqué et al, 2019;Hawkings et al, 2020). Similarly to Si/Na*, Ge/Na* indicates Ge depletion, requiring uptake by secondary phases ( Figure 4E).…”

Section: Field Signaturessupporting

confidence: 75%

Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland

et al. 2021

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Glacial environments offer the opportunity to study the incipient stages of chemical weathering due to the high availability of finely ground sediments, low water temperatures, and typically short rock-water interaction times. In this study we focused on the geochemical behavior of germanium (Ge) in west Greenland, both during subglacial weathering by investigating glacier-fed streams, as well as during a batch reactor experiment by allowing water-sediment interaction for up to 2 years in the laboratory. Sampled in late August 2014, glacial stream Ge and Si concentrations were low, ranging between 12–55 pmol/L and 7–33 µmol/L, respectively (Ge/Si = 0.9–2.2 µmol/mol, similar to parent rock). As reported previously, the dissolved stable Ge isotope ratio (δ74Ge) of the Watson River was 0.86 ± 0.24‰, the lowest among global rivers and streams measured to date. This value was only slightly heavier than the suspended load (0.48 ± 0.23‰), which is likely representative of the bulk parent rock composition. Despite limited Ge/Si and δ74GeGe fractionation, both Ge and Si appear depleted relative to Na during subglacial weathering, which we interpret as the relatively congruent uptake of both phases by amorphous silica (aSi). Continued sediment-water interaction over 470–785 days in the lab produced a large increase in dissolved Si concentrations (up to 130–230 µmol/L), a much smaller increase in dissolved Ge (up to ∼70 pmol/L), resulting in a Ge/Si decrease (to 0.4–0.5 µmol/mol) and a significant increase in δ74Ge (to 1.9–2.2‰). We argue that during the experiment, both Si and Ge are released by the dissolution of previously subglacially formed aSi, and Ge is then incorporated into secondary phases (likely adsorbed to Fe oxyhydroxides), with an associated Δ74Gesecondary−dissolved fractionation factor of −2.15 ± 0.46‰. In summary, we directly demonstrate Ge isotope fractionation during the dissolution-precipitation weathering reactions of natural sediments in the absence of biological Ge and Si uptake, and highlight the significant differences in Ge behavior during subglacial and non-glacial weathering.

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“…The majority of subglacial weathering budgets are based purely on the dissolved major ion ratios of glacial outflow, with enhanced sulfate and bicarbonate ion concentrations indicating that the dominant weathering pathways beneath glaciers are carbonate dissolution and sulfide oxidation (M. Torres et al, 2017; Tranter et al, 2002; Urra et al, 2019). These combined weathering reactions ultimately release CO 2 to the atmosphere, leading to the idea that glacial weathering processes could help to stabilize net cooling feedbacks during glacial periods (Sharp et al, 1995; M. Torres et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

The Influence of Glacial Cover on Riverine Silicon and Iron Exports in Chilean Patagonia

Pryer

Hawkings

Wadham

et al. 2020

Global Biogeochemical Cycles

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Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (<0.02 μm) concentrations were relatively low in glacier-fed rivers, whereas concentrations of colloidal-nanoparticulate (0.02-0.45 μm) Si and Fe increased significantly as a function of glacial cover. These colloidal-nanoparticulate phases were predominately composed of aluminosilicates and Fe-oxyhydroxides, highlighting the need for size-fractionated analyses and further research to quantify the lability of colloidal-nanoparticulate species. We also demonstrate the importance of reactive particulate (>0.45 μm) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems. Glacial weathering processes have been identified to be particularly important in the generation of potentially bioavailable iron (Fe) (

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Weathering Dynamics Under Contrasting Greenland Ice Sheet Catchments

Cited by 19 publications

References 77 publications

Silicon Isotopic Composition of Dry and Wet-Based Glaciers in Antarctica

Silicon Isotopic Composition of Dry and Wet-Based Glaciers in Antarctica

Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland

The Influence of Glacial Cover on Riverine Silicon and Iron Exports in Chilean Patagonia

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