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Silicon Isotopes Reveal a Non-Glacial Source of Silicon to Crescent Stream, Mcmurdo Dry Valleys, Antarctica

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Hirst, C., Opfergelt, S., Gaspard, F., Hendry, K., Hatton, J., Welch, S., Mcknight, D., & Lyons, W. B. (2020). Silicon isotopes reveal a non- glacial source of silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica. Frontiers in Marine Science, 8, [229]. https://doi.org/10.3389/feart.2020.00229 Publisher's PDF, also known as Version of record License (if available): CC BY Link to published version (if available): 10.3389/feart.2020.00229 Link to publication record in Explore Bristol Research PDF-document This is the final published version of the article (version of record). It first appeared online via Frontiers Media at https://www.frontiersin.org/articles/10.3389/feart.2020.00229/full. Please refer to any applicable terms of use of the publisher. University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ feart-08-00229 June 26, 2020 Time: 15:43 # 1 ORIGINAL RESEARCH published: 26 June 2020 doi: 10.3389/feart.2020.00229 Silicon Isotopes Reveal a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica Catherine Hirst1*, Sophie Opfergelt1, François Gaspard1, Katharine R. Hendry2, Jade E. Hatton2, Susan Welch3, Diane M. McKnight4 and W. Berry Lyons3 1 Earth and Life Institute, Environmental Sciences, Université catholique de Louvain, Louvain-la-Neuve, Belgium, 2 School of Earth Sciences, University of Bristol, Bristol, United Kingdom, 3 School of Earth Sciences, Byrd Polar and Climate Research Center, The Ohio State University, Columbus, OH, United States, 4 Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, United States In high latitude environments, silicon is supplied to river waters by both glacial and non- glacial chemical weathering. The signal of these two end-members is often obscured by biological uptake and/or groundwater input in the river catchment. McMurdo Dry Edited by: Valleys streams in Antarctica have no deep groundwater input, no connectivity between Andrew Jonathan Hodson, The University Centre in Svalbard, streams and no surface vegetation cover, and thus provide a simplified system for us Norway to constrain the supply of dissolved silicon (DSi) to rivers from chemical weathering in Reviewed by: a glacial environment. Here we report dissolved Si concentrations, germanium/silicon Yigal Erel, 30 Hebrew University of Jerusalem, Israel ratios (Ge/Si) and silicon isotope compositions (d SiDSi) in Crescent Stream, McMurdo Martin Guitreau, Dry Valleys for samples collected between December and February in the 2014−2015, Université Clermont Auvergne, France 30 2015−2016, and 2016−2017 austral seasons. The d SiDSi compositions and DSi *Correspondence: concentrations are higher than values reported in wet-based glacial meltwaters, and Catherine Hirst [email protected] form a narrow cluster within the range of values reported for permafrost dominated 30 Arctic Rivers. High d SiDSi compositions, ranging from C0.90 to C1.39 , are Specialty section: attributed to (i) the precipitation of amorphous silica during freezingh of waters in isolatedh This article was submitted to Geochemistry, pockets of the hyporheic zone in the winter and the release of Si from unfrozen a section of the journal pockets during meltwater-hyporheic zone exchange in the austral summer, and (ii) Frontiers in Earth Science additional Si isotope fractionation via long-term Si uptake in clay minerals and seasonal Received: 09 March 2020 Accepted: 28 May 2020 Si uptake into diatoms superimposed on this winter-derived isotope signal. There is 30 Published: 26 June 2020 no relationship between d SiDSi compositions and DSi concentrations with seasonal Citation: and daily discharge, showing that stream waters contain DSi that is in equilibrium with Hirst C, Opfergelt S, Gaspard F, the formation of secondary Si minerals in the hyporheic zone. We show that d30Si Hendry KR, Hatton JE, Welch S, DSi McKnight DM and Berry Lyons W compositions can be used as tracers of silicate weathering in the hyporheic zone and (2020) Silicon Isotopes Reveal possible tracers of freeze-thaw conditions in the hyporheic zone. This is important in a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry the context of the ongoing warming in McMurdo Dry Valleys and the supply of more Valleys, Antarctica. meltwaters to the hyporheic zone of McMurdo Dry Valley streams. Front. Earth Sci. 8:229. doi: 10.3389/feart.2020.00229 Keywords: silicon isotopes, hyporheic zone, permafrost, weathering, Antarctica Frontiers in Earth Science| www.frontiersin.org 1 June 2020| Volume 8| Article 229 feart-08-00229 June 26, 2020 Time: 15:43 # 2 Hirst et al. Silicon Isotopes in Crescent Stream INTRODUCTION hyporheic zone and near-stream hyporheic zone? To answer these questions we use dissolved silicon isotope composition 30 McMurdo Dry Valleys (MDV), the largest ice-free area of (d SiDSi) and the germanium/silicon ratios (Ge/Si) to pull Antarctica, is covered in continuous permafrost, with low surface apart primary silicate weathering processes, biotic processes temperatures and low rates of precipitation. Under these polar and abiotic secondary weathering processes in a permafrost- desert conditions, groundwater and surface soil water reservoirs dominated stream in Antarctica. 30 are absent (Conovitz et al., 1998), and first-order streams and The d SiDSi composition of river waters reflect the processes their surrounding hyporheic zones are isolated conduits for occurring after silicate mineral dissolution (Opfergelt and supra-glacial meltwater transport and a loci of weathering (Lyons Delmelle, 2012; Frings et al., 2016) resulting from secondary et al., 1998; McKnight et al., 1998, 1999, 2004). mineral formation and dissolution (Georg et al., 2006), A wealth of evidence using dissolved element concentrations adsorption of Si onto Al and Fe (oxy)hydroxides (Delstanche and ratios (Lyons et al., 1998; Nezat et al., 2001), Sr and Li isotope et al., 2009; Oelze et al., 2014), diatom uptake (Alleman et al., analysis (Lyons et al., 2002; Witherow et al., 2010; Dowling et al., 2005; Opfergelt et al., 2011) and dissolution (Demarest et al., 2013) and mineralogical studies (Gooseff et al., 2002; Maurice 2009; Egan et al., 2012; Wetzel et al., 2014) and phytolith et al., 2002) shows that Si is supplied to the streams by weathering formation (Opfergelt et al., 2008) and dissolution (Ziegler et al., of stream sediments with silicate mineral weathering rates an 2005) in vascular plants during dissolved silicon transport in 30 order of magnitude greater than rates in lower latitude, warmer the river basin. At present, d SiDSi compositions in large Arctic locations (Gooseff et al., 2002). These studies demonstrate that rivers are used to constrain the drivers of terrestrial-ocean chemical weathering of silicates occurs in MDV streams (Lyons silicon supply in high latitude permafrost-dominated systems 30 et al., 2002), despite the cold temperatures, lack of precipitation with an average flux-weighted Arctic River d SiDSi composition and low abundance of complexing organic material (Burkins of C1.3 (Pokrovsky et al., 2013; Mavromatis et al., 2016; 30 et al., 2001), and thereby contribute to the atmospheric CO2 draw Sun et al.h, 2018). During winter months, d SiDSi compositions down over geological timescales (Berner and Berner, 1997). are higher than average values, attributed to aluminosilicate Taylor Valley streams in MDV are characterized by extensive dissolution and secondary mineral precipitation in groundwater 30 hyporheic zones, which comprise the sediment pore spaces systems (Pokrovsky et al., 2013). During spring flood, the d SiDSi adjacent to and underneath the stream through which stream compositions are lower than or similar to silicate rock values, water exchanges. This zone also is the accommodation space that attributed to the dissolution of suspended matter within rivers must be filled before stream flow occurs. Mineral dissolution and leaching of biomass (Pokrovsky et al., 2013; Mavromatis 30 in the hyporheic zone is the commonly accepted contributor et al., 2016; Sun et al., 2018). During summer months, d SiDSi to stream geochemistry (Gooseff et al., 2002), but the model compositions show a wide range in values resulting from Si of Gooseff et al.(2002) assumes no precipitation reactions of uptake into vascular plants and phytoplankton alongside the secondary weathering products, including only the net release mixing of tributaries with different Si isotope compositions of solutes from weathering reactions. Secondary weathering (Sun et al., 2018). In these large river basins, the role of products such as clay minerals may form, but the extent to secondary mineral precipitation and its impact on riverine 30 which this occurs within streams is unknown (Lyons et al., d SiDSi compositions is often obscured by biological and plant 1998; Gooseff et al., 2002). Considering only the net release of uptake and/or mixing of surface and sub-surface waters in solutes from weathering reactions, and not accounting for the the river basin. formation of secondary weathering products in the near and The simplified and well characterized MDV streams, with extended hyporheic zone in MDV streams may contribute to an no vegetation and no groundwater supply to streams, provides underestimation of actual
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