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Basal ice at the margin of the Greenland ice sheet was studied with respect to its physical characteristics and microbiological community. The basal ice contained high concentrations of dissolved ferrous Fe and must therefore be anoxic. Oxygen consumption experiments indicate that 50% of the oxidation was due to biological activity while the rest c...
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... 2005). However, although it is now generally accepted that basal ice provides habitats for metabolizing microorganism communities (Sharp and others, 1999; Skidmore and others, 2000; Sheridan and others, 2003; Miteva and others, 2004; Tung and others, 2006; Yung and others, 2007), an understanding of the role of microorganisms in basal ice facies is only in its infancy. This paper presents the results of the first study on the microbial community and its potential activities in basal ice at the margin of the Greenland ice sheet (GIS), West Greenland. The focus of our study is on the microbial community in the lowest basal ice facies, referred to as the solid ice facies. We also describe the physical characteristics of the basal ice environment, so that this study may be compared to similar basal ice microbiology studies in order to determine what subglacial processes influence the microbial community structure in various basal ice facies. The study site (67 8 08 21 N, 50 8 02 43 W; 490 m a.s.l.) is located between the outlet glaciers Isunguata Sermia and Russell Glacier at the margin of the GIS (Fig. 1). The climate is continental low Arctic and the region is considered to be a polar desert (Hobbs, 1931). The nearest meteorological station is located at the airport of Kangerlussuaq (Søndre Strømfjord), $ 31 km west of the study area. Here the mean annual air temperature and the mean annual precipitation are –5.7 8 C and 149 mm (1961–90), respectively (Cappelen, 2009). There is continuous permafrost, with an active layer thickness of $ 0.5 m in peat-covered areas and >1.0 m on unvegetated proglacial outwash plains. The geology consists of amphibolite and granulite facies gneisses with deformed and boudinaged basic to intermediate intrusive dykes belonging to the Nagssugtoqidian mobile belt (Escher and others, 1976). The ice margin at the study site is relatively stable and has maintained its position at least since the Little Ice Age. During the 1968–2002 advance of parts of the ice margin (Knight and others, 2007), the studied section of the ice margin is believed to have increased in ice thickness, whereas since 2002 ice thickness has decreased. For this study, a vertical basal ice profile was selected at a location where ice flow was perpendicular to the ice margin and all primary basal ice facies were accessible. There were no signs of deformation, thrusting or duplication in the profile that might unnecessarily complicate the basal ice stratigraphy. Also, the site was not affected by the recent major jo ̈ kulhlaups that drained an ice-dammed lake located 1 km westwards (A.J. Russell and others, unpublished information). The stratigraphic log of the basal ice profile is shown in Figure 2. The profile has a thickness of 1.20 m and contains ten ice units defined by internal ...
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... At higher taxonomic levels, the composition of exported microbial assemblages from the CH 4 release hotspot site was comparable to those previously found in subglacial meltwaters [20,[45][46][47] and sediments [2,48,49]. However, in contrast to most previous studies, we observed a remarkable prevalence of ASVs affiliated with methylotrophic genera. ...
Subglacial environments provide conditions suitable for the microbial production of methane, an important greenhouse gas, which can be released from beneath the ice as a result of glacial melting. High gaseous methane emissions have recently been discovered at Russell Glacier, an outlet of the southwestern margin of the Greenland Ice Sheet, acting not only as a potential climate amplifier but also as a substrate for methane consuming microorganisms. Here, we describe the composition of the microbial assemblage exported in meltwater from the methane release hotspot at Russell Glacier and its changes over the melt season and as it travels downstream. We found that a substantial part (relative abundance 27.2% across the whole dataset) of the exported assemblage was made up of methylotrophs and that the relative abundance of methylotrophs increased as the melt season progressed, likely due to the seasonal development of the glacial drainage system. The methylotrophs were dominated by representatives of type I methanotrophs from the Gammaproteobacteria; however, their relative abundance decreased with increasing distance from the ice margin at the expense of type II methanotrophs and/or methylotrophs from the Alphaproteobacteria and Betaproteobacteria. Our results show that subglacial methane release hotspot sites can be colonized by microorganisms that can potentially reduce methane emissions.
... They are found in subglacial water at concentrations ranging from 1 × 10 2 to 1 × 10 5 cells mL −1 Sheridan et al., 2003;Grasby et al., 2003) and are even more abundant in subglacial sediment at concentrations of 10 6 to 10 7 cells g −1 of sediment (Sharp et al., 1999;Lanoil et al., 2009). Studies consistently find that among these cells exists a metabolically active microbial community that is of-ten phylogenetically and functionally diverse Yde et al., 2010;Christner et al., 2014;Hamilton et al., 2013). Some of these subglacial ecosystems are sustained by reservoirs of organic matter (Hood et al., 2015) acquired as glaciers override soil and vegetation (Christ et al., 2021), marine deposits (Wadham et al., 2012;Michaud et al., 2016), and organic-rich shales (Wadham et al., 2004;Grasby et al., 2003) or from the in-wash of supraglacial or ice-marginal organic matter (Tranter et al., 2005;Andrews et al., 2018). ...
... Primary production in many subglacial ecosystems is dominated by lithotrophic microbial metabolisms (Kayani et al., 2018;Boyd et al., 2014;Christner et al., 2014;Dunham et al., 2021), in which organisms utilize solutes or elements from the underlying bedrock to liberate chemical energy. Microbially mediated redox reactions in subglacial systems occur via the oxidation of reduced inorganic compounds such as ferrous iron (Fe 2+ ), sulfide (S 2− ), hydrogen (H 2 ), ammonium (NH + 4 ), and methane (CH 4 ) coupled to the reduction in species such as oxygen (O 2 ), nitrate (NO − 3 ), carbon dioxide (CO 2 ), or sulfate (SO 2− 4 ) (Miteva et al., 2004;Boyd et al., 2011Boyd et al., , 2014Yde et al., 2010;Stibal et al., 2012a;Wadham et al., 2004;Tranter et al., 2002;Dunham et al., 2021;Achberger et al., 2016;Christner et al., 2014;Michaud et al., 2017). Glacial comminution serves to liberate and in some cases even produce Macdonald et al., 2018;Gill-Olivas et al., 2021) redox-sensitive species for subglacial ecosystems. ...
... Simulations that incorporated basal solutes improved the accuracy of modelled solute concentrations, though the accuracy of the models was inconsistent among geochemically relevant compounds (Fig. 5a). The solute composition of basal ice, subglacial water, and species liberated from in situ rock weathering can vary dramatically within a subglacial catchment (Dubnick et al., 2020;Yde et al., 2010;Tranter et al., 2002) due to variation in the composition of the underlying bedrock, redox conditions, ice and water temperatures, and freeze-thaw histories. The five basal ice samples explored in this study also showed high variability in solute chemistry (Fig. 4), confirming that potential basal solute sources in the subglacial tunnel are heterogeneous and that our model may not accurately represent the precise composition of the basal solutes entering the pond. ...
Subglacial environments comprise ∼10 % of Earth's land surface, host active microbial ecosystems, and are important components of global biogeochemical cycles. However, the broadly inaccessible nature of subglacial systems has left them vastly understudied, and research to date has been limited to laboratory experiments or field measurements using basal ice or subglacial water accessed through boreholes or from the glacier margin. In this study, we extend our understanding of subglacial biogeochemistry and microbiology to include observations of a slushy pond of water that occupied a remnant meltwater channel beneath a polythermal glacier in the Canadian High Arctic over winter. The hydraulics and geochemistry of the system suggest that the pond water originated as late-season, ice-marginal runoff with less than ∼15 % solute contribution from subglacial sources. Over the 8 months of persistent sub-zero regional temperatures, the pond gradually froze, cryo-concentrating solutes in the residual water by up to 7 times. Despite cryo-concentration and the likely influx of some subglacial solute, the pond was depleted in only the most labile and biogeochemically relevant compounds, including ammonium, phosphate, and dissolved organic matter, including a potentially labile tyrosine-like component. DNA amplicon sequencing revealed decreasing microbial diversity with distance into the meltwater channel. The pond at the terminus of the channel hosted a microbial community inherited from late-season meltwater, which was dominated by only six taxa related to known psychrophilic and psychrotolerant heterotrophs that have high metabolic diversity and broad habitat ranges. Collectively, our findings suggest that generalist microbes from the extraglacial or supraglacial environments can become established in subglacial aquatic systems and deplete reservoirs of nutrients and dissolved organic carbon over a period of months. These findings extend our understanding of the microbial and biogeochemical evolution of subglacial aquatic ecosystems and the extent of their habitability.
... While few measurements of such ice have been made, these layers visually contain a high sediment load and have been shown to contain cells (i.e., 10 2 to 10 4 cell g -1 ) (Montross et al., 2014). The introduction of cellular debris, organic matter, and nutrients located in the basal layer (Skidmore et al., 2000;Wadham et al., 2004Wadham et al., , 2008Tung et al., 2005;Yde et al., 2010;Doyle, 2014) could inadvertently influence the subglacial realm, changing the microbial ecology and geochemical parameters. This type of forward contamination is addressed in the Antarctic CoC, which states that ''drilling in conjunction with sampling procedures will inevitably introduce microorganisms into the subglacial aquatic environments. ...
Ocean Worlds beneath thick ice covers in our solar system, as well as subglacial lakes on Earth, may harbor biological systems. In both cases, thick ice covers (>100 s of meters) present significant barriers to access. Melt probes are emerging as tools for reaching and sampling these realms due to their small logistical footprint, ability to transport payloads, and ease of cleaning in the field. On Earth, glaciers are immured with various abundances of microorganisms and debris. The potential for bioloads to accumulate around and be dragged by a probe during descent has not previously been investigated. Due to the pristine nature of these environments, minimizing and understanding the risk of forward contamination and considering the potential of melt probes to act as instrument-induced special regions are essential. In this study, we examined the effect that two engineering descent strategies for melt probes have on the dragging of bioloads. We also tested the ability of a field cleaning protocol to rid a common contaminant, Bacillus. These tests were conducted in a synthetic ice block immured with bioloads using the Ice Diver melt probe. Our data suggest minimal dragging of bioloads by melt probes, but conclude that modifications for further minimization and use in special regions should be made.
... They are found in subglacial water at concentrations ranging from 1 x 35 10 2 to 1 x 10 5 cells ml -1 (Christner et al., 2014;Sheridan et al., 2003;Grasby et al., 2003) and are even more abundant in subglacial sediment at concentrations of 10 6 to 10 7 cells g -1 of sediment (Sharp et al., 1999;Lanoil et al., 2009). Studies consistently find that among these cells exists a metabolically-active microbial community that is often phylogenetically and functionally diverse (Vick-Majors et al., 2016;Yde et al., 2010;Christner et al., 2014;Hamilton et al., 2013). Some of these subglacial ecosystems are sustained by reservoirs of organic matter (Hood et al., 2015) acquired as glaciers override soil and 40 vegetation (Christ et al., 2021), marine deposits (Wadham et al., 2012;Michaud et al., 2016), and organic-rich shales (Wadham et al., 2004;Grasby et al., 2003), or from the in-wash of supraglacial or ice-marginal organic matter (Tranter et al., 2005;Andrews et al., 2018). ...
... Primary production in many subglacial ecosystems is dominated by lithotrophic microbial metabolisms (Kayani et al., 2018;45 Boyd et al., 2014;Christner et al., 2014;Dunham et al., 2021), in which organisms utilize solutes or elements from the underlying bedrock to liberate chemical energy. Microbially-mediated redox reactions in subglacial systems occur via the oxidation of reduced inorganic compounds such as ferrous iron (Fe 2+ ), sulfide (S 2-), hydrogen (H2), ammonium (NH4 + ), and methane (CH4,) coupled to the reduction of species such as oxygen (O2), nitrate (NO3 -), carbon dioxide (CO2), or sulfate (SO4 2-) (Miteva et al., 2004;Boyd et al., 2011;Yde et al., 2010;Stibal et al., 2012a;Wadham et al., 2004;Tranter et al., 2002;Boyd 50 et al., 2014;Dunham et al., 2021;Achberger et al., 2016;Christner et al., 2014;Michaud et al., 2017). Glacial comminution serves to liberate, and in some cases even produce (Telling et al., 2015;Macdonald et al., 2018;Gill-Olivas et al., 2021), redoxsensitive species for subglacial ecosystems. ...
... Simulations that incorporated basal solutes improved the accuracy of modeled solute concentrations, though the accuracy of the models were inconsistent among geochemically-relevant compounds (Figure 5a). The solute composition of basal ice, subglacial water, and species liberated from in situ rock weathering, can vary dramatically within a subglacial catchment 450 (Dubnick et al., 2020;Yde et al., 2010;Tranter et al., 2002) due to variation in the composition of the underlying bedrock, redox conditions, ice/water temperatures, and freeze-thaw histories. The five basal ice samples explored in this study also showed high variability in solute chemistry (Figure 4), confirming that potential basal solute sources in the subglacial tunnel are heterogeneous and that our model may not accurately represent the precise composition of the basal solutes entering the pond. ...
Subglacial environments comprise ~10 % of Earth’s land surface, host active microbial ecosystems, and are important components of global biogeochemical cycles. However, the broadly inaccessible nature of subglacial systems has left them vastly understudied, and research to date has been limited to laboratory experiments or field measurements using basal ice or subglacial water accessed through boreholes or from the glacier margin. In this study, we extend our understanding of subglacial biogeochemistry and microbiology to include observations of a slushy pond of water that occupied a remnant meltwater channel beneath a polythermal glacier in the Canadian High Arctic over winter. The hydraulics and geochemistry of the system suggest that the pond water originated as late-season, ice-marginal runoff with less than ~15 % solute contribution from subglacial sources. Over the eight months of persistent sub-zero regional temperatures, the pond gradually froze, cryo-concentrating solutes in the residual water by up to seven times. Despite cryo-concentration and the likely influx of some subglacial solute, the pond was depleted in only the most labile and biogeochemically-relevant compounds, including ammonium, phosphate, and dissolved organic matter, including a potentially labile tyrosine-like component. DNA amplicon sequencing revealed decreasing microbial diversity with distance into the meltwater channel. The pond at the terminus of the channel hosted a microbial community inherited from late-season meltwater, which was dominated by only six taxa related to known psychrophilic/psychrotolerant heterotrophs that have high metabolic diversity and broad habitat ranges. Collectively, our findings suggest that generalist microbes from the extraglacial or supraglacial environments can become established in subglacial aquatic systems and deplete reservoirs of nutrients and dissolved organic carbon over a period of months. These findings extend our understanding of the microbial and biogeochemical evolution of subglacial aquatic ecosystems and the extent of their habitability.
... This ranges from relatively debrispoor types containing < 1 % (w/v) sediment to debris-rich types composed almost entirely of sediment with only interstitial ice (Knight, 1997). When compared to the overlying englacial ice (i.e., derived from snowfall), the sediment-rich basal ice contains higher concentrations of potential microbial substrates that include formate, acetate, ferrous iron, and ammonia (Skidmore et al., 2000;Wadham et al., 2004;Tung et al., 2006;Yde et al., 2010). These compounds are hypothesized to be an important source of electron donors for heterotrophic and lithotrophic microorganisms inhabiting subglacial environments, including frozen matrices within the basal ice itself (Montross et al., 2014. ...
... Positive and negative associations are black and red, respectively. (Yde et al., 2010;Skidmore et al., 2005;Cheng and Foght, 2007;Katayama et al., 2007;Steven et al., 2008) compared to the "indicator" lineages we identified in Fig. 4. To achieve this, we inserted full-length clone sequences into the metaanalysis reference tree using SEPP and taxonomically classified them using Wang's Bayesian inference method with the Silva v.138.1 database as a reference. Clone sequences were then agglomerated together with meta-analysis ASVs belonging to the same genera. ...
Glaciers and ice sheets possess basal ice layers characterized by high amounts of entrained debris that can serve as sources of nutrients and organic matter, providing a habitat for microorganisms adapted to the frozen conditions. Basal ice forms through various mechanisms and is classified based on ice and debris content; however, little is known about variation in microbial composition, diversity, and activity across different basal ice types. We investigated these parameters in four different types of basal ice from a cold-based and temperate glacier and used a meta-analysis to compare our findings with microbiome studies from other frozen environments. We found basal ice environments harbor a diverse range of microbiomes whose composition and activity can vary significantly between basal ice types, even within adjacent facies from the same glacier. In some debris-rich basal ices, elevated ATP concentrations, isotopic gas signatures, and high 16S rRNA/rDNA amplicon ratios implicated certain bacterial taxa (e.g., Paenisporosarcina, Desulfocapsa, Syntrophus, and Desulfosporosinus) as being potentially active, with ice temperature appearing to be an important predictor for the diversity of inferred active taxa. Compared to those of other sympagic environments, the basal ice microbiomes more closely resemble those found in permafrost or perennial cave ice than glacial ice. In contrast, debris-poor basal ices harbored microbiomes more like those found in englacial ice. Collectively, these results suggest that different basal ice types contain distinct microbiomes that are actively structured by physicochemical properties of their habitat.
... However, recent studies on microbiology have revealed the presence of diverse and complex microorganisms in glacial ice from Antarctica, the Arctic, Greenland, and Tibet (Takeuchi et al., 2001;Takeuchi, 2002;Zhang et al., 2002;Karr et al., 2005). Although studies have investigated glacier microorganisms, most have focused disproportionately on specific locations or parts of glacial ice (Tung et al., 2006;Miteva et al., 2009;Yde et al., 2010). Studies on glacial microbes have shown that microbial diversity differs depending on the origin, location, and depth of the glacier, suggesting that a study covering various regions and the entire glacial ice is necessary to understand and conceptualize glacial biogeography. ...
... The glacier surface shows a relatively high level of microbial cell abundance (0-2,600 × 10 3 cells/ml) compared with snow (Amato et al., 2007;Irvine-Fynn et al., 2012;Stibal et al., 2015). Glacial ice has an abundance of 0.02-7 × 10 3 cells/ml (Tung et al., 2005;Zhang et al., 2008aZhang et al., , 2008bMiteva et al., 2009;Santibáñez et al., 2018), and basal ice has a wider abundance range of 0.1 × 10 3 to 30.6 × 10 7 cells/ml (Sheridan et al., 2003;Yde et al., 2010;Montross et al., 2014). ...
Glaciers, formed from the gradual accumulation of snow, can be continuous records representing past environments and recognized as a time capsule of our planetary evolution. Due to extremely harsh conditions, glacial ice has long been considered an uninhabitable ecosystem for microorganisms to sustain their life. However, recent developments in microbiological analysis techniques revealed the presence of unexpectedly diverse microbial strains. Glacial microorganisms could also provide valuable information, including not only biological diversity and structure but also molecular systematics, metabolic profiles, and evolutionary changes from the past climate and ecosystem. However, there are several obstacles in investigating the glacier environment, such as low regional accessibility, technical difficulties of ice coring, potential contamination during the sampling process, and low microbial biomass. This review aims to summarize recent knowledge on decontamination methods, biomass, diversity based on culture-dependent and -independent methods, application of biological proxies, greenhouse gas production and adaptive strategies in glaciers from various regions and to imply further directions for a comprehensive understanding of habitatility in an icy world including outer of our planet.
... The subglacial environment has received much less attention but is thought to be important for bedrock-derived mineral substrate weathering and the release of nutrients into the proglacial environment as mineral-bearing debris melts out from the ice Rime et al., 2016). Subglacial environments are characterized by low temperature, absence of light, oligotrophic conditions, and high mineral content (Bakermans & Skidmore, 2011;Montross et al., 2014;Yde et al., 2010), which suggests that chemolithotrophic metabolisms could play a fundamental role in subglacial ecosystems (Boyd et al., 2014;Christner et al., 2014;Mitchell et al., 2013). ...
... At Taylor Glacier, Antarctica, a BI cell content of 2.5 x 10 2 to 1.2 x 10 4 g ml −1 was found, and 7.9 x 10 6 cells g −1 existed within basal sediment (Montross et al., 2014;; 8.7 x 10 5 cells g −1 were found in Russell Glacier (Greenland) (Stibal, Hasan, et al., 2012); 1.7 -6.8 x 10 5 cells g −1 were found in Finsterwalderbreen, Svalbard (Lawson et al., 2015); and 1.3 -1.4 x 10 7 cells g −1 were found in Svínafellsjökull, Iceland (Toubes-Rodrigo et al., 2016). Subglacial environments have been shown to foster an abundance of chemolithotrophic-associated microorganisms (Boyd et al., 2014;Yde et al., 2010). For example, Mitchell et al., (2013) reported that bacterial Fe-and S-oxidizers were abundant in subglacial meltwater discharge from Robertson Glacier, Canada and that microorganisms were more abundant in minerals that could be easily oxidized, such as pyrite. ...
... Acknowledging that PICRUSt metabolic modeling is not exempt from caveats and that this simulation is not a substitute for metatranscriptomics, we decided to use it to build a hypothesis of the potential metabolism present in BI. Figure 7 shows that the predicted metabolism in BI is dominated by chemosynthesis over photosynthesis (16.2% vs 7.3% of energy-related KOs; Welch t-test p-value <0.01), which is not surprising given the lack of light in the subglacial environment (Yde et al., 2010). Recent research has shown a high abundance of genes associated with ribulose bisphosphate carboxylase (RuBiSCO) in BI, which supports our hypothesis that BI is driven by chemolithotrophy (Kayani et al., 2018). ...
The basal zone of glaciers is characterized by physicochemical properties that are distinct from firnified ice due to strong interactions with underlying substrate and bedrock. Basal ice (BI) ecology and the roles that the microbiota play in biogeochemical cycling, weathering, and proglacial soil formation remain poorly described. We report on basal ice geochemistry, bacterial diversity (16S rRNA gene phylogeny), and inferred ecological roles at three temperate Icelandic glaciers. We sampled three physically distinct basal ice facies (stratified, dispersed, and debris bands) and found facies dependent on biological similarities and differences; basal ice character is therefore an important sampling consideration in future studies. Based on a high abundance of silicates and Fe-containing minerals and, compared to earlier BI literature, total C was detected that could sustain the basal ice ecosystem. It was hypothesized that C-fixing chemolithotrophic bacteria, especially Fe-oxidisers and hydrogenotrophs, mutualistically support associated heterotrophic communities. Basal ice-derived rRNA gene sequences corresponding to genera known to harbor hydrogenotrophic methanogens suggest that silicate comminution-derived hydrogen can also be utilized for methanogenesis. PICRUSt-predicted metabolism suggests that methane metabolism and C-fixation pathways could be highly relevant in BI, indicating the importance of these metabolic routes. The nutrients and microbial communities release from melting basal ice may play an important role in promoting pioneering communities establishment and soil development in deglaciating forelands.
... A number of studies have found that (nano)particulates dominate the export of potentially (co-)limiting nutrients such as iron (Fe), phosphorus (P), and silica (Si) from glacial systems (Raiswell et al., 2006;Hawkings et al., 2015;Hawkings et al., 2017). If labile and bioavailable, this material may serve as an important source of nutrients for the subglacial and marine offshore ecosystems (Yde et al., 2010;Gerringa et al., 2012;Lawson et al., 2014;Meire et al., 2016;Vick-Majors et al., 2020). ...
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 δ 74 G e Ge 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.
... The subglacial environment has received much less attention, but is thought to be important for substrate weathering and the release of nutrients into the proglacial environment as mineral-bearing debris melts out from the ice Rime et al., 2016). Subglacial environments are characterised by low temperature, absence of light, oligotrophic conditions, and high mineral content (Yde et al., 2010;Bakermans and Skidmore, 2011;Montross et al., 2014), which suggests that subglacial ecosystems are dominated by microbial chemolithotrophic metabolisms (Mitchell et al., 2013;Boyd et al., 2014;Christner et al., 2014). ...
... At Taylor Glacier, Antarctica, a BI cell content of 2.5 x 10 2 to 1.2 x 10 4 g ml -1 was found, and 7.9 x 10 6 cells g -1 existed within basal sediment (Stibal, Hasan, et al., 2012;Montross et al., 2014); 8.7 x 10 5 cells g -1 were found in Russell Glacier (Greenland) (Stibal, Hasan, et al., 2012); 1.7 -6.8 x 10 5 cells g -1 were found in Finsterwalderbreen, Svalbard (Lawson et al., 2015); and 1.3 -1.4 x 10 7 cells g -1 were found in Svínafellsjökull, Iceland (Toubes-Rodrigo, S J Cook, et al., 2016). Subglacial environments have been shown to foster an abundance of chemolithotrophic-associated microorganisms (Yde et al., 2010;Boyd et al., 2014). For example, Mitchell et al. (2013) reported that bacterial Fe-and S-oxidisers were abundant in subglacial meltwater discharge from Robertson Glacier, Canada, and that microorganisms were more abundant in minerals that could be easily oxidised, such as pyrite. ...
... Acknowledging that PICRUSt is not exempt from caveats, and that this simulation is not substitute of metatranscriptomics, we decided to use it in order to build a hypothesis about the potential metabolisms in BI. Fig 7 shows that BI is dominated by chemosynthesis over photosynthesis (16.2% vs 7.3% of energy-related KOs; Welch t-test p-value < 0.01), which is not surprising given the lack of light in the subglacial environment (Yde et al., 2010). Recent research has shown a high abundance of genes associated with ribulose bisphosphate carboxylase (RuBiSCO) in BI, which supports our hypothesis that BI is driven by chemolithotrophy (Kayani et al., 2018). ...
The basal zone of glaciers is characterised by physicochemical properties that are distinct from firnified ice because of strong interactions with underlying substrate. Basal ice ecology and the roles that the microbiota play in biogeochemical cycling, weathering, and proglacial soil formation, remains poorly known. We report bacterial diversity and potential ecological roles at three temperate Icelandic glaciers. We sampled three physically distinct basal ice facies (stratified, dispersed, debris bands) and found biological similarities and differences between them; basal ice character is therefore an important sampling consideration in future studies. High abundance of silicates and Fe-containing minerals could sustain the basal ice ecosystem, in which chemolithotrophic bacteria (~23%), especially Fe-oxidisers and hydrogenotrophs, can fix C, which can be utilised by heterotrophs. Methanogenic-affiliated detected sequences showed that silicate comminution-derived hydrogen can also be utilised for methanogenesis. Metabolism predicted by 16S rRNA diversity revealed that methane metabolism and C-fixation are the most common pathways, indicating the importance of these metabolic routes. Carbon concentrations were low compared to other ecosystems, but we report the highest carbon concentration in basal ice to date. Carbon release from melting basal ice may play an important role in promoting pioneering communities establishment and soil development in deglaciating forelands.
... These removal processes were first detected in glacial runoff by Wadham et al. (2004) and Wynn et al. (2006), but geochemical evidence that these reactions are important beneath ice sheets is presently slow to emerge. Early examples include analyses of basal ice from the margins of the Greenland Ice Sheet (e.g., Yde et al., 2010) and the wet till slurries beneath Whillans Ice Stream in Antarctica (Mikucki et al., 2016). The latter work demonstrates how molecular evidence for the relevant microbial consortia is often better developed than the geochemical evidence from meltwaters. ...
The geochemistry of glacial outflows is best developed in the case of valley glaciers, where more than four decades of research have provided major insights into solute acquisition and biogeochemical processes. This chapter describes these processes and draws important distinctions between valley glaciers and larger, less understood polar ice sheets. Key reactions that define the composition of glacial outflows are described, giving emphasis to their major ion, nutrient, stable isotope and minor or trace element composition. Qualitative and quantitative attempts to use this information to separate glacial outflow hydrographs into delayed (distributed) and rapid (channelized) flow paths are also described.
