The silicon cycle impacted by past ice sheets

Hawkings, Jon R.; Hatton, Jade E.; Hendry, Katharine R.; Souza, Gregory F. de; Wadham, Jemma L.; Ivanovic, Ruza; Kohler, Tyler J.; Stibal, Marek; Beaton, Alexander; Lamarche-Gagnon, Guillaume; Tedstone, Andrew; Hain, Mathis P.; Bagshaw, Elizabeth; Pike, Jennifer; Tranter, Martyn

doi:10.1038/s41467-018-05689-1

Cited by 38 publications

(83 citation statements)

References 84 publications

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“…Opfergelt et al (2013) reported glacial rivers to have a mean composition of 0.17 ± 0.18‰ compared to 0.97 ± 0.31‰ for non-glacial rivers. The dissolved phase exported from a large ice sheet catchment of GrIS has also been shown to have an isotopic composition lighter than the bulk bedrock (-0.25 ± 0.12‰ compared to 0.00 ± 0.07‰, Hawkings et al, 2018). These studies indicate that subglacial processes could be influencing the isotopic composition of meltwaters.…”

Section: Introductionmentioning

confidence: 76%

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

Hatton

Hendry

Hawkings

et al. 2019

Geochimica et Cosmochimica Acta

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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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Section: Introductionmentioning

confidence: 76%

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

Hatton

Hendry

Hawkings

et al. 2019

Geochimica et Cosmochimica Acta

Self Cite

100

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“…The discharge ( Q ) record was constructed by creating a rating curve between stage and discharge measured using rhodamine dye traces over the full range of river stages as described in Hawkings et al (). Specific conductivity (SpC), pH, and turbidity were recorded every 15 min using a Campbell data logger.…”

Section: Methodsmentioning

confidence: 99%

Glacier Outflow Dissolved Organic Matter as a Window Into Seasonally Changing Carbon Sources: Leverett Glacier, Greenland

et al. 2020

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The Greenland Ice Sheet is losing mass at a remarkable rate as a result of climatic warming.This mass loss coincides with the export of dissolved organic matter (DOM) in glacial meltwaters. However, little is known about how the source and composition of exported DOM changes over the melt season, which is key for understanding its fate in downstream ecosystems. Over the 2015 ablation season, we sampled the outflow of Leverett Glacier, a large land-terminating glacier of the Greenland Ice Sheet. Dissolved organic carbon (DOC) concentrations and DOM fluorescence were analyzed to assess the evolution of DOM sources over the course of the melt season. DOC concentrations and red-shifted fluorescence were highly associated (R 2 > 0.95) and suggest terrestrial inputs from overridden soils dominated DOM early season inputs before progressive dilution with increasing discharge. During the outburst period, supraglacial drainage events disrupted the subglacial drainage system and introduced dominant protein-like fluorescence signatures not observed in basal flow. These results suggest that subglacial hydrology and changing water sources influence exported DOC concentration and DOM composition, and these sources were differentiated using fluorescence characteristics. Red-shifted fluorescence components were robust proxies for DOC concentration. Finally, the majority of DOM flux, which occurs during the outburst and postoutburst periods, was characterized by protein-like fluorescence from supraglacial and potentially subglacial microbial sources. As protein-like fluorescence is linked to the bioavailability of DOM, the observed changes likely reflect seasonal variations in the impact of glacial inputs on secondary production in downstream ecosystems due to shifting hydrologic regimes.

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“…And you can heat up spacetimes by collapsing matter or even by just accelerating [10]. The horizons which arise in general relativity are endowed with temperatures [11] which shows that, at least in this context, some microscopic degrees of freedom are coming into play. So a thermodynamic description that links the standard description of gravity with the statistical mechanics of -as yet unknownmicroscopic degrees of freedom must exist.…”

Section: What Is It All About?mentioning

confidence: 99%

A dialogue on the nature of gravity

Padmanabhan¹

2012

Foundations of Space and Time

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I describe the conceptual and mathematical basis of an approach which describes gravity as an emergent phenomenon. Combining the principle of equivalence and the principle of general covariance with known properties of local Rindler horizons, perceived by observers accelerated with respect to local inertial frames, one can provide a thermodynamic reinterpretation of the field equations describing gravity in any diffeomorphism invariant theory. This fact, in turn, leads us to the possibility of deriving the field equations of gravity by maximising a suitably defined entropy functional, without using the metric tensor as a dynamical variable. The approach synthesizes concepts from quantum theory, thermodynamics and gravity leading to a fresh perspective on the nature of gravity. The description is presented here in the form of a dialogue, thereby addressing several frequently-asked-questions.

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The silicon cycle impacted by past ice sheets

Cited by 38 publications

References 84 publications

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

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

Glacier Outflow Dissolved Organic Matter as a Window Into Seasonally Changing Carbon Sources: Leverett Glacier, Greenland

A dialogue on the nature of gravity

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