<p><b>Table 5.</b> Sequencing depth and diversity and dominance indices for th... more <p><b>Table 5.</b> Sequencing depth and diversity and dominance indices for the selected samples of cryoconite from Aldegondabreen. </p> <p><strong>Abstract</strong></p> <p>The aggregation of surface debris particles on melting glaciers into larger units (cryoconite) provides microenvironments for various microorganisms and metabolic processes. Here we investigate the microbial community on the surface of Aldegondabreen, a valley glacier in Svalbard which is supplied with carbon and nutrients from different sources across its surface, including colonies of seabirds. We used a combination of geochemical analysis (of surface debris, ice and meltwater), quantitative polymerase chain reactions (targeting the 16S ribosomal ribonucleic acid and <em>amoA</em> genes), pyrosequencing and multivariate statistical analysis to suggest possible factors driving the ecology of prokaryotic microbes on the surface of Aldegondabreen and their potential role in nitrogen cycling. The combination of high nutrient input with subsidy from the bird colonies, supraglacial meltwater flow and the presence of fine, clay-like particles supports the formation of centimetre-scale cryoconite aggregates in some areas of the glacier surface. We show that a diverse microbial community is present, dominated by the cyanobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria, that are well-known in supraglacial environments. Importantly, ammonia-oxidizing archaea were detected in the aggregates for the first time on an Arctic glacier.</p
The composition and spatial variability of microbial communities that reside within the extensive... more The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km 2) biologically active area encompassing the Greenland ice sheet (GrIS) is hypothesized to be variable. We examined bacterial communities from cryoconite debris and surface ice across the GrIS, using sequence analysis and quantitative PCR of 16S rRNA genes from co-extracted DNA and RNA. Communities were found to differ across the ice sheet, with 82.8% of the total calculated variation attributed to spatial distribution on a scale of tens of kilometers separation. Amplicons related to Sphingobacteriaceae, Pseudanabaenaceae and WPS-2 accounted for the greatest portion of calculated dissimilarities. The bacterial communities of ice and cryoconite were moderately similar (global R = 0.360, P = 0.002) and the sampled surface type (ice versus cryoconite) did not contribute heavily towards community dissimilarities (2.3% of total variability calculated). The majority of dissimilarities found between cryoconite 16S rRNA gene amplicons from DNA and RNA was calculated to be the result of changes in three taxa, Pseudanabaenaceae, Sphingobacteriaceae and WPS-2, which together contributed towards 80.8 ± 12.6% of dissimilarities between samples. Bacterial communities across the GrIS are spatially variable active communities that are likely influenced by localized biological inputs and physicochemical conditions.
Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindri... more Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, such as tardigrades and rotifers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances but rather a positive correlation with eukaryotic microalgae. Shared environmental preferences and a positive effect of grazing are the proposed mechanisms to explain these correlations. Most microalgae found in this study form colonies (< 10 cells, or > 25 µm), which may protect them against invertebrate grazing. This finding rather indicates grazing as a positive control on eukaryotic microalgae by nutrient recycling. Density differences between the eukaryotic microalgae and prokaryotic cyanobacteria and their high distinction in redundancy (RDA) and principal component (PCA) analyses indicate that these two groups are in strong contrast. Eukaryotic microalgae occurred mainly in unstable cryoconite holes with high sediment loads, high N : P ratios, and a high impact of nutrient input by bird guano, as a proxy for nutrients. In these environments autochthonous nitrogen fixation appears to be negligible. Selective wind transport of Oscillatoriales via soil and dust particles is proposed to explain their dominance in cryoconites further away from the glacier margins. We propose that, for the studied glaciers, nutrient levels related to recycling of limiting nutrients are the main factor driving variation in the community structure of microalgae and grazers.
&amp;lt;p&amp;gt;Glaciers and ice sheets cover around 10% of the Earth&amp;amp;#8217;... more &amp;lt;p&amp;gt;Glaciers and ice sheets cover around 10% of the Earth&amp;amp;#8217;s surface and the Greenland Ice Sheet (GrIS) is the largest ice mass in the Northern hemisphere, but is melting at an increasing rate, losing ~400 km&amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt; annually. There have been recent studies linking subglacial environments of the GrIS with methane (CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) production and release, presenting a possible positive climate feedback. Previous work has linked organic carbon in subglacial environments with significant CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; export via methanogenesis. It has been hypothesised that the GrIS overlies a methanogenically active wetland environment, and thus needs to be included in the global CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; budget.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;However, the subglacial system of the GrIS is complex and highly heterogenous, hosting oxic and anoxic ecosystems, which have developed over a range of timescales. There are still questions outstanding surrounding the ubiquity of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release from the GrIS, mainly because of the limited understanding of subglacial carbon cycling and the potential sources of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; in these environments. &amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We present the first data from two new, complimentary projects investigating CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release from the GrIS margin, where we aim to quantify the production and release of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; into the atmosphere from the GrIS. We have developed an ambitious temporal and spatial sampling regime to evaluate the CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release along the western margin of the GrIS. We present the first radiocarbon (&amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C) dated CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; samples from Greenland, helping to shed light on the carbon cycling processes occurring under the ice sheet. We analyse a mixture of atmospheric CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; exported from subglacial ice caves and dissolved CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; from proglacial rivers draining subglacial portals to explore the age of subglacially sourced CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We can combine the carbon age of exported CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; with microbial analysis and stable isotope data to improve our understanding of the environmental controls on and microbial sources of subglacial CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; production and export. Understanding the mechanisms behind subglacial CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; export is crucial when attempting to upscale the point source data that is available currently and we consider whether the GrIS could be a potentially important source of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, leading to a substantial, yet currently understudied climatic feedback.&amp;lt;/p&amp;gt;
Glacial environments play an important role in high-latitude marine nutrient cycling, potentially... more Glacial environments play an important role in high-latitude marine nutrient cycling, potentially contributing significant fluxes of silicon (Si) to the polar oceans, either as dissolved silicon (DSi) or dissolvable amorphous silica (ASi). Silicon is a key nutrient in promoting marine primary productivity, contributing to atmospheric CO<sub>2</sub> removal. We present the current understanding of Si cycling in glacial systems, focusing on the Si isotope (δ<sup>30</sup>Si) composition of glacial meltwaters. We combine existing glacial δ<sup>30</sup>Si data with new measurements from twenty sub-Arctic glaciers, showing that glacial meltwaters consistently export isotopically light DSi compared to non-glacial rivers (+0.16‰ versus +1.38‰). Glacial δ<sup>30</sup>Si<sub>ASi</sub> composition ranges from −0.05‰ to −0.86‰ but exhibits low seasonal variability. Silicon fluxes and δ<sup>30</sup>Si composition from glacial systems are not commonly included in global Si budgets and isotopic mass balance calculations at present. We discuss outstanding questions, including the formation mechanism of ASi and the export of glacial nutrients from fjords. Finally, we provide a contextual framework for the recent advances in our understanding of subglacial Si cycling and highlight critical research avenues for assessing potential future changes in these environments.
Cryoconite holes are small, extreme habitats, widespread in the ablation zones of gla-ciers world... more Cryoconite holes are small, extreme habitats, widespread in the ablation zones of gla-ciers worldwide. They can provide a suitable environment for microorganisms including bacteria, cyanobacteria, algae, fungi, and invertebrates. Diatoms have been previously recovered from cryoconite holes of Greenland and of Svalbard, and recent findings from Antarctica suggest that cryoconite holes may harbor a unique diatom flora distinct from other aquatic habitats nearby. In the present study, we characterize the diatom communi-ties of Nordenskiöld glacier cryoconite holes in Billefjorden (Svalbard, Spitsbergen), and multivariate approaches were used to compare them with three freshwater localities in the immediate vicinity to investigate possible sources of the species pool. We found cryoconite holes to have similar or greater average genus-richness than adjacent lake/ ponds habitats, even though lower numbers of valves were recovered. Overall, cryoconite hole diatom communities differed signi...
Ice sheets overlay active and putatively widespread microbial ecosystems. An active subglacial bi... more Ice sheets overlay active and putatively widespread microbial ecosystems. An active subglacial biota has the potential to impact strongly on the (bio)geochemistry of local as well as downstream environments. Such impacts partly depend on the distribution of microbial populations, the types of habitats present beneath the ice, and their connectivity. In the ablation zone of the Greenland Ice Sheet (GrIS), supraglacial meltwaters are routed to the ice-sheet bed during the melt season, flushing out subglacial waters, sediments, and cells to proglacial environments via runoff. Here, we report on the diversity, composition, and niche differentiation of microbial assemblages exported in bulk runoff from a large (~600 km 2) GrIS catchment. Proglacial river samples were collected over a period of subglacial drainage evolution in order to capture potential shifts in exported microbial community alongside hydrochemical transitions. We use high-resolution hydrochemical and hydrological information from the proglacial river to guide microbial (16S rRNA gene) interpretations. Core populations closely matched sequences previously isolated from other (pro)glacial environments, and phylogenetic characterisation of main OTUs alluded to a central role for subglacial iron, sulphur, and methane cycling. Whilst results indicate that bulk populations exported are likely true members of sub ice-sheet communities, we also find evidence of a supraglacial signature influencing composition of exported assemblages. Changes in assemblage structure accompanied those of major hydrological periods, with enhanced subglacial flushing coinciding with distinct shifts in microbial composition. Timing of sampling therefore matters when attempting to infer more nuanced changes in exported communities, or reveal the biogeochemical processes likely occurring in regions of the bed less influenced by surface melt. This is likely especially true when studying larger glacial systems, which experience complex hydrological changes throughout the melt-season, and that periods of. CC-BY-NC-ND 4.
Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it ... more Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate. We hypothesized that older POC is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer. To test this, POC samples were collected from a meltwater river exiting the GrIS over an ablation season and 14 C dated. Resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area. We found that POC ages increased from~5000 tõ 9000 years B.P. until peak discharge and catchment size. Afterward, significant fluctuations in POC age were observed, interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion. These observations suggest a seasonal progression in the source of POC exported from the GrIS and provide evidence for a seasonally evolving subglacial drainage system.
Measuring microbial abundance in glacier ice and identifying its controls is essential for a bett... more Measuring microbial abundance in glacier ice and identifying its controls is essential for a better understanding and quantification of biogeochemical processes in glacial ecosystems. However, cell enumeration of glacier ice samples is challenging due to typically low cell numbers and the presence of interfering mineral particles. We quantified for the first time the abundance of microbial cells in surface ice from geographically distinct sites on the Greenland Ice Sheet (GrIS), using three enumeration methods: epifluorescence microscopy (EFM), flow cytometry (FCM), and quantitative polymerase chain reaction (qPCR). In addition, we reviewed published data on microbial abundance in glacier ice and tested the three methods on artificial ice samples of realistic cell (10 2-10 7 cells ml −1) and mineral particle (0.1-100 mg ml −1) concentrations, simulating a range of glacial ice types, from clean subsurface ice to surface ice to sediment-laden basal ice. We then used multivariate statistical analysis to identify factors responsible for the variation in microbial abundance on the ice sheet. EFM gave the most accurate and reproducible results of the tested methodologies, and was therefore selected as the most suitable technique for cell enumeration of ice containing dust. Cell numbers in surface ice samples, determined by EFM, ranged from ∼ 2 × 10 3 to ∼ 2 × 10 6 cells ml −1 while dust concentrations ranged from 0.01 to 2 mg ml −1. The lowest abundances were found in ice sampled from the accumulation area of the ice sheet and in samples affected by fresh snow; these samples may be considered as a reference point of the cell abundance of precipitants that are deposited on the ice sheet surface. Dust content was the most significant variable to explain the variation in the abundance data, which suggests a direct association between deposited dust particles and cells and/or by their provision of limited nutrients to microbial communities on the GrIS.
Glacial ice covers around 10% of the Earth's continents. A review of the literature suggests ... more Glacial ice covers around 10% of the Earth's continents. A review of the literature suggests that microbes living on glaciers and ice sheets are an integral part of both the glacial environment and the Earth's ecosystem.
This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License New... more This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License Newcastle University ePrints-eprint.ncl.ac.uk
Recent studies have shown the release of methane (CH4) through the melting Greenland Ice Sheet, ... more Recent studies have shown the release of methane (CH4) through the melting Greenland Ice Sheet, and have thus identified it to have an additional potential positive climate feedback. This CH4 is thought to originate from biologically active methanogenic ecosystems in subglacial sediments, where microbes produce it by converting overridden organic carbon to CH4, which then accumulates over time. Subsequent CH4 diffusion into the subglacial hydrologic network transports it then to the ice sheet margin, where it is directly emitted to the atmosphere from supersaturated proglacial streams. Methanogenesis is highly dependent on anoxic conditions, which are in turn determined by the seasonally evolving subglacial environment subject to episodic flooding and thereby recharging oxygenated waters from surface melting. The main biogeochemical and hydrological drivers influencing the rate of CH4 production, as well as the magnitude and timing of these subglacial CH4 fluxes remain largely unknown and therefore unconstrained. Addressing these unknowns is essential because CH4 is not only a powerful greenhouse gas, but also because its unaccounted release exacerbates the ongoing climate amplification in the Arctic. The lack of observational data is primarily due to the challenging conditions for accessing the subglacial environment and the shortage of direct measurements of CH4 production, consumption, and export from the Greenland Ice Sheet and the complex nature of the subglacial system. This invites the application of reaction-transport modelling tools in combination with observational data to fill these knowledge gaps by disentangling the complex processes and drivers, and eventually quantifying CH4 cycling processes in Greenland’s subglacial sediments and their impacts on the global CH4 cycle and climate change. However, such modelling tools do not currently exist. Here, we develop a coupled subglacial sediment-cavity-stream model to explore the potential of subglacial environments to produce and accumulate methane beneath the Greenland Ice shield. The model accounts for heterotrophic methane production, methane oxidation, as well as advective and diffusive methane transport. Current field data observations are used to initialize the model, but it will also be forced over a wide range of plausible conditions (i.e. organic matter availability and reactivity, sediment thickness, terminal electron acceptor availability) that have could be found beneath the Greenland Ice shield. The results of this large model ensemble does not only help identify the most important biogeochemical and hydrological drivers on methane production and accumulation in subglacial environments, but also allows to identify areas beneath the ice sheet that could produce and accumulate important quantities of methane.These new developments present the first step in the development of a new fully coupled hydrological-biogeochemical model for subglacial environments, which will inform upscaling efforts and guide future field work.
During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vege... more During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vegetation and buried significant stores of organic matter (OM); these glaciers are now shrinking rapidly due to climate warming. Little is known about the biogeochemical processing of the OM buried beneath glacier ice which makes the processes associated with deglaciation difficult to predict. Subglacial sediments exposed at receding glacier fronts may represent a legacy of past biogeochemical processes. Here, we analyzed sediments from retreating fronts of 19 Arctic glaciers for their mineralogical and elemental composition, contents of major nutrients, OM biomarkers (aliphatic lipids and lignin‐derived phenols), 14C age, and microbial community structure. We show the character of the sediments is mostly determined by local glaciation history and bedrock lithology. Most subglacial sediments offer high amounts of readily bioavailable phosphorus (i.e., loose, labile, and Fe/Al P fractions) but lack readily accessible carbon substrates. The subglacial OM originated mainly from overridden terrestrial vascular plants. The results of OM biomarker analysis and 14C dating suggest the OM substrates degrade in the subglacial environment and are reworked by the resident microbial communities. We argue the biogeochemical legacy of the perishing subglacial environments is an important determinant for the early processes of proglacial ecological succession.
Microbes transported by glacial meltwater streams are thought to be a product of passive dispersa... more Microbes transported by glacial meltwater streams are thought to be a product of passive dispersal from both supra- and subglacial sources, though studies investigating the origins of these assemblages are scarce. Here, we conducted a survey within a large catchment containing multiple glaciers on Qeqertarsuaq (Disko Island), west Greenland, to investigate whether meltwater-exported microbial assemblages in suspended sediments differ between glacial meltwater streams, and if they reflect corresponding bulk subglacial and extraglacial sediment communities. Using 16S rRNA gene amplicon sequencing, we found proglacial stream assemblages substantially differ from one another, despite their close spatial proximity. Furthermore, proglacial stream assemblages were composed of greater proportions of Cyanobacteria compared to bulk subglacial sediment communities, dominated by Betaproteobacteria, demonstrating large contributions of meltwater and microbial cells from supraglacial habitats. Co...
Proglacial streams export large quantities of both supraand subglacially-derived microbial cells,... more Proglacial streams export large quantities of both supraand subglacially-derived microbial cells, which have been suggested to play functional and nutritional roles in downstream, estuarine, and coastal habitats. Despite the widespread retreat of northern hemisphere glaciers, very little work has investigated possible environmental controls on the assemblage structure of glacial meltwater streams, and to date no studies have made broad comparisons between different regions of the Arctic. Here, we address two key questions: 1) are glacial meltwater microbial assemblages similar between major Arctic (and sub-Arctic) regions, and 2) can variability within these regions be explained by the physical and chemical characteristics of individual drainage basins?
Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindri... more Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered as hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances, but a positive correlation with eukaryotic microalgae. Most microalgae found in this study form large colonies (< 10 cells, or > 25 μm), which may protect them against invertebrate grazing. This findi...
<p><b>Table 5.</b> Sequencing depth and diversity and dominance indices for th... more <p><b>Table 5.</b> Sequencing depth and diversity and dominance indices for the selected samples of cryoconite from Aldegondabreen. </p> <p><strong>Abstract</strong></p> <p>The aggregation of surface debris particles on melting glaciers into larger units (cryoconite) provides microenvironments for various microorganisms and metabolic processes. Here we investigate the microbial community on the surface of Aldegondabreen, a valley glacier in Svalbard which is supplied with carbon and nutrients from different sources across its surface, including colonies of seabirds. We used a combination of geochemical analysis (of surface debris, ice and meltwater), quantitative polymerase chain reactions (targeting the 16S ribosomal ribonucleic acid and <em>amoA</em> genes), pyrosequencing and multivariate statistical analysis to suggest possible factors driving the ecology of prokaryotic microbes on the surface of Aldegondabreen and their potential role in nitrogen cycling. The combination of high nutrient input with subsidy from the bird colonies, supraglacial meltwater flow and the presence of fine, clay-like particles supports the formation of centimetre-scale cryoconite aggregates in some areas of the glacier surface. We show that a diverse microbial community is present, dominated by the cyanobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria, that are well-known in supraglacial environments. Importantly, ammonia-oxidizing archaea were detected in the aggregates for the first time on an Arctic glacier.</p
The composition and spatial variability of microbial communities that reside within the extensive... more The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km 2) biologically active area encompassing the Greenland ice sheet (GrIS) is hypothesized to be variable. We examined bacterial communities from cryoconite debris and surface ice across the GrIS, using sequence analysis and quantitative PCR of 16S rRNA genes from co-extracted DNA and RNA. Communities were found to differ across the ice sheet, with 82.8% of the total calculated variation attributed to spatial distribution on a scale of tens of kilometers separation. Amplicons related to Sphingobacteriaceae, Pseudanabaenaceae and WPS-2 accounted for the greatest portion of calculated dissimilarities. The bacterial communities of ice and cryoconite were moderately similar (global R = 0.360, P = 0.002) and the sampled surface type (ice versus cryoconite) did not contribute heavily towards community dissimilarities (2.3% of total variability calculated). The majority of dissimilarities found between cryoconite 16S rRNA gene amplicons from DNA and RNA was calculated to be the result of changes in three taxa, Pseudanabaenaceae, Sphingobacteriaceae and WPS-2, which together contributed towards 80.8 ± 12.6% of dissimilarities between samples. Bacterial communities across the GrIS are spatially variable active communities that are likely influenced by localized biological inputs and physicochemical conditions.
Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindri... more Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, such as tardigrades and rotifers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances but rather a positive correlation with eukaryotic microalgae. Shared environmental preferences and a positive effect of grazing are the proposed mechanisms to explain these correlations. Most microalgae found in this study form colonies (< 10 cells, or > 25 µm), which may protect them against invertebrate grazing. This finding rather indicates grazing as a positive control on eukaryotic microalgae by nutrient recycling. Density differences between the eukaryotic microalgae and prokaryotic cyanobacteria and their high distinction in redundancy (RDA) and principal component (PCA) analyses indicate that these two groups are in strong contrast. Eukaryotic microalgae occurred mainly in unstable cryoconite holes with high sediment loads, high N : P ratios, and a high impact of nutrient input by bird guano, as a proxy for nutrients. In these environments autochthonous nitrogen fixation appears to be negligible. Selective wind transport of Oscillatoriales via soil and dust particles is proposed to explain their dominance in cryoconites further away from the glacier margins. We propose that, for the studied glaciers, nutrient levels related to recycling of limiting nutrients are the main factor driving variation in the community structure of microalgae and grazers.
&amp;lt;p&amp;gt;Glaciers and ice sheets cover around 10% of the Earth&amp;amp;#8217;... more &amp;lt;p&amp;gt;Glaciers and ice sheets cover around 10% of the Earth&amp;amp;#8217;s surface and the Greenland Ice Sheet (GrIS) is the largest ice mass in the Northern hemisphere, but is melting at an increasing rate, losing ~400 km&amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt; annually. There have been recent studies linking subglacial environments of the GrIS with methane (CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) production and release, presenting a possible positive climate feedback. Previous work has linked organic carbon in subglacial environments with significant CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; export via methanogenesis. It has been hypothesised that the GrIS overlies a methanogenically active wetland environment, and thus needs to be included in the global CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; budget.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;However, the subglacial system of the GrIS is complex and highly heterogenous, hosting oxic and anoxic ecosystems, which have developed over a range of timescales. There are still questions outstanding surrounding the ubiquity of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release from the GrIS, mainly because of the limited understanding of subglacial carbon cycling and the potential sources of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; in these environments. &amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We present the first data from two new, complimentary projects investigating CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release from the GrIS margin, where we aim to quantify the production and release of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; into the atmosphere from the GrIS. We have developed an ambitious temporal and spatial sampling regime to evaluate the CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; release along the western margin of the GrIS. We present the first radiocarbon (&amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C) dated CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; samples from Greenland, helping to shed light on the carbon cycling processes occurring under the ice sheet. We analyse a mixture of atmospheric CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; exported from subglacial ice caves and dissolved CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; from proglacial rivers draining subglacial portals to explore the age of subglacially sourced CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We can combine the carbon age of exported CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; with microbial analysis and stable isotope data to improve our understanding of the environmental controls on and microbial sources of subglacial CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; production and export. Understanding the mechanisms behind subglacial CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; export is crucial when attempting to upscale the point source data that is available currently and we consider whether the GrIS could be a potentially important source of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, leading to a substantial, yet currently understudied climatic feedback.&amp;lt;/p&amp;gt;
Glacial environments play an important role in high-latitude marine nutrient cycling, potentially... more Glacial environments play an important role in high-latitude marine nutrient cycling, potentially contributing significant fluxes of silicon (Si) to the polar oceans, either as dissolved silicon (DSi) or dissolvable amorphous silica (ASi). Silicon is a key nutrient in promoting marine primary productivity, contributing to atmospheric CO<sub>2</sub> removal. We present the current understanding of Si cycling in glacial systems, focusing on the Si isotope (δ<sup>30</sup>Si) composition of glacial meltwaters. We combine existing glacial δ<sup>30</sup>Si data with new measurements from twenty sub-Arctic glaciers, showing that glacial meltwaters consistently export isotopically light DSi compared to non-glacial rivers (+0.16‰ versus +1.38‰). Glacial δ<sup>30</sup>Si<sub>ASi</sub> composition ranges from −0.05‰ to −0.86‰ but exhibits low seasonal variability. Silicon fluxes and δ<sup>30</sup>Si composition from glacial systems are not commonly included in global Si budgets and isotopic mass balance calculations at present. We discuss outstanding questions, including the formation mechanism of ASi and the export of glacial nutrients from fjords. Finally, we provide a contextual framework for the recent advances in our understanding of subglacial Si cycling and highlight critical research avenues for assessing potential future changes in these environments.
Cryoconite holes are small, extreme habitats, widespread in the ablation zones of gla-ciers world... more Cryoconite holes are small, extreme habitats, widespread in the ablation zones of gla-ciers worldwide. They can provide a suitable environment for microorganisms including bacteria, cyanobacteria, algae, fungi, and invertebrates. Diatoms have been previously recovered from cryoconite holes of Greenland and of Svalbard, and recent findings from Antarctica suggest that cryoconite holes may harbor a unique diatom flora distinct from other aquatic habitats nearby. In the present study, we characterize the diatom communi-ties of Nordenskiöld glacier cryoconite holes in Billefjorden (Svalbard, Spitsbergen), and multivariate approaches were used to compare them with three freshwater localities in the immediate vicinity to investigate possible sources of the species pool. We found cryoconite holes to have similar or greater average genus-richness than adjacent lake/ ponds habitats, even though lower numbers of valves were recovered. Overall, cryoconite hole diatom communities differed signi...
Ice sheets overlay active and putatively widespread microbial ecosystems. An active subglacial bi... more Ice sheets overlay active and putatively widespread microbial ecosystems. An active subglacial biota has the potential to impact strongly on the (bio)geochemistry of local as well as downstream environments. Such impacts partly depend on the distribution of microbial populations, the types of habitats present beneath the ice, and their connectivity. In the ablation zone of the Greenland Ice Sheet (GrIS), supraglacial meltwaters are routed to the ice-sheet bed during the melt season, flushing out subglacial waters, sediments, and cells to proglacial environments via runoff. Here, we report on the diversity, composition, and niche differentiation of microbial assemblages exported in bulk runoff from a large (~600 km 2) GrIS catchment. Proglacial river samples were collected over a period of subglacial drainage evolution in order to capture potential shifts in exported microbial community alongside hydrochemical transitions. We use high-resolution hydrochemical and hydrological information from the proglacial river to guide microbial (16S rRNA gene) interpretations. Core populations closely matched sequences previously isolated from other (pro)glacial environments, and phylogenetic characterisation of main OTUs alluded to a central role for subglacial iron, sulphur, and methane cycling. Whilst results indicate that bulk populations exported are likely true members of sub ice-sheet communities, we also find evidence of a supraglacial signature influencing composition of exported assemblages. Changes in assemblage structure accompanied those of major hydrological periods, with enhanced subglacial flushing coinciding with distinct shifts in microbial composition. Timing of sampling therefore matters when attempting to infer more nuanced changes in exported communities, or reveal the biogeochemical processes likely occurring in regions of the bed less influenced by surface melt. This is likely especially true when studying larger glacial systems, which experience complex hydrological changes throughout the melt-season, and that periods of. CC-BY-NC-ND 4.
Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it ... more Surface melt from the Greenland Ice Sheet (GrIS) collects particulate organic carbon (POC) as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate. We hypothesized that older POC is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer. To test this, POC samples were collected from a meltwater river exiting the GrIS over an ablation season and 14 C dated. Resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area. We found that POC ages increased from~5000 tõ 9000 years B.P. until peak discharge and catchment size. Afterward, significant fluctuations in POC age were observed, interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion. These observations suggest a seasonal progression in the source of POC exported from the GrIS and provide evidence for a seasonally evolving subglacial drainage system.
Measuring microbial abundance in glacier ice and identifying its controls is essential for a bett... more Measuring microbial abundance in glacier ice and identifying its controls is essential for a better understanding and quantification of biogeochemical processes in glacial ecosystems. However, cell enumeration of glacier ice samples is challenging due to typically low cell numbers and the presence of interfering mineral particles. We quantified for the first time the abundance of microbial cells in surface ice from geographically distinct sites on the Greenland Ice Sheet (GrIS), using three enumeration methods: epifluorescence microscopy (EFM), flow cytometry (FCM), and quantitative polymerase chain reaction (qPCR). In addition, we reviewed published data on microbial abundance in glacier ice and tested the three methods on artificial ice samples of realistic cell (10 2-10 7 cells ml −1) and mineral particle (0.1-100 mg ml −1) concentrations, simulating a range of glacial ice types, from clean subsurface ice to surface ice to sediment-laden basal ice. We then used multivariate statistical analysis to identify factors responsible for the variation in microbial abundance on the ice sheet. EFM gave the most accurate and reproducible results of the tested methodologies, and was therefore selected as the most suitable technique for cell enumeration of ice containing dust. Cell numbers in surface ice samples, determined by EFM, ranged from ∼ 2 × 10 3 to ∼ 2 × 10 6 cells ml −1 while dust concentrations ranged from 0.01 to 2 mg ml −1. The lowest abundances were found in ice sampled from the accumulation area of the ice sheet and in samples affected by fresh snow; these samples may be considered as a reference point of the cell abundance of precipitants that are deposited on the ice sheet surface. Dust content was the most significant variable to explain the variation in the abundance data, which suggests a direct association between deposited dust particles and cells and/or by their provision of limited nutrients to microbial communities on the GrIS.
Glacial ice covers around 10% of the Earth's continents. A review of the literature suggests ... more Glacial ice covers around 10% of the Earth's continents. A review of the literature suggests that microbes living on glaciers and ice sheets are an integral part of both the glacial environment and the Earth's ecosystem.
This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License New... more This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License Newcastle University ePrints-eprint.ncl.ac.uk
Recent studies have shown the release of methane (CH4) through the melting Greenland Ice Sheet, ... more Recent studies have shown the release of methane (CH4) through the melting Greenland Ice Sheet, and have thus identified it to have an additional potential positive climate feedback. This CH4 is thought to originate from biologically active methanogenic ecosystems in subglacial sediments, where microbes produce it by converting overridden organic carbon to CH4, which then accumulates over time. Subsequent CH4 diffusion into the subglacial hydrologic network transports it then to the ice sheet margin, where it is directly emitted to the atmosphere from supersaturated proglacial streams. Methanogenesis is highly dependent on anoxic conditions, which are in turn determined by the seasonally evolving subglacial environment subject to episodic flooding and thereby recharging oxygenated waters from surface melting. The main biogeochemical and hydrological drivers influencing the rate of CH4 production, as well as the magnitude and timing of these subglacial CH4 fluxes remain largely unknown and therefore unconstrained. Addressing these unknowns is essential because CH4 is not only a powerful greenhouse gas, but also because its unaccounted release exacerbates the ongoing climate amplification in the Arctic. The lack of observational data is primarily due to the challenging conditions for accessing the subglacial environment and the shortage of direct measurements of CH4 production, consumption, and export from the Greenland Ice Sheet and the complex nature of the subglacial system. This invites the application of reaction-transport modelling tools in combination with observational data to fill these knowledge gaps by disentangling the complex processes and drivers, and eventually quantifying CH4 cycling processes in Greenland’s subglacial sediments and their impacts on the global CH4 cycle and climate change. However, such modelling tools do not currently exist. Here, we develop a coupled subglacial sediment-cavity-stream model to explore the potential of subglacial environments to produce and accumulate methane beneath the Greenland Ice shield. The model accounts for heterotrophic methane production, methane oxidation, as well as advective and diffusive methane transport. Current field data observations are used to initialize the model, but it will also be forced over a wide range of plausible conditions (i.e. organic matter availability and reactivity, sediment thickness, terminal electron acceptor availability) that have could be found beneath the Greenland Ice shield. The results of this large model ensemble does not only help identify the most important biogeochemical and hydrological drivers on methane production and accumulation in subglacial environments, but also allows to identify areas beneath the ice sheet that could produce and accumulate important quantities of methane.These new developments present the first step in the development of a new fully coupled hydrological-biogeochemical model for subglacial environments, which will inform upscaling efforts and guide future field work.
During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vege... more During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vegetation and buried significant stores of organic matter (OM); these glaciers are now shrinking rapidly due to climate warming. Little is known about the biogeochemical processing of the OM buried beneath glacier ice which makes the processes associated with deglaciation difficult to predict. Subglacial sediments exposed at receding glacier fronts may represent a legacy of past biogeochemical processes. Here, we analyzed sediments from retreating fronts of 19 Arctic glaciers for their mineralogical and elemental composition, contents of major nutrients, OM biomarkers (aliphatic lipids and lignin‐derived phenols), 14C age, and microbial community structure. We show the character of the sediments is mostly determined by local glaciation history and bedrock lithology. Most subglacial sediments offer high amounts of readily bioavailable phosphorus (i.e., loose, labile, and Fe/Al P fractions) but lack readily accessible carbon substrates. The subglacial OM originated mainly from overridden terrestrial vascular plants. The results of OM biomarker analysis and 14C dating suggest the OM substrates degrade in the subglacial environment and are reworked by the resident microbial communities. We argue the biogeochemical legacy of the perishing subglacial environments is an important determinant for the early processes of proglacial ecological succession.
Microbes transported by glacial meltwater streams are thought to be a product of passive dispersa... more Microbes transported by glacial meltwater streams are thought to be a product of passive dispersal from both supra- and subglacial sources, though studies investigating the origins of these assemblages are scarce. Here, we conducted a survey within a large catchment containing multiple glaciers on Qeqertarsuaq (Disko Island), west Greenland, to investigate whether meltwater-exported microbial assemblages in suspended sediments differ between glacial meltwater streams, and if they reflect corresponding bulk subglacial and extraglacial sediment communities. Using 16S rRNA gene amplicon sequencing, we found proglacial stream assemblages substantially differ from one another, despite their close spatial proximity. Furthermore, proglacial stream assemblages were composed of greater proportions of Cyanobacteria compared to bulk subglacial sediment communities, dominated by Betaproteobacteria, demonstrating large contributions of meltwater and microbial cells from supraglacial habitats. Co...
Proglacial streams export large quantities of both supraand subglacially-derived microbial cells,... more Proglacial streams export large quantities of both supraand subglacially-derived microbial cells, which have been suggested to play functional and nutritional roles in downstream, estuarine, and coastal habitats. Despite the widespread retreat of northern hemisphere glaciers, very little work has investigated possible environmental controls on the assemblage structure of glacial meltwater streams, and to date no studies have made broad comparisons between different regions of the Arctic. Here, we address two key questions: 1) are glacial meltwater microbial assemblages similar between major Arctic (and sub-Arctic) regions, and 2) can variability within these regions be explained by the physical and chemical characteristics of individual drainage basins?
Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindri... more Glaciers are known to harbor surprisingly complex ecosystems. On their surface, distinct cylindrical holes filled with meltwater and sediments are considered as hot spots for microbial life. The present paper addresses possible biological interactions within the community of prokaryotic cyanobacteria and eukaryotic microalgae (microalgae) and relations to their potential grazers, additional to their environmental controls. Svalbard glaciers with substantial allochthonous input of material from local sources reveal high microalgal densities. Small valley glaciers with high sediment coverages and high impact of birds show high biomasses and support a high biological diversity. Invertebrate grazer densities do not show any significant negative correlation with microalgal abundances, but a positive correlation with eukaryotic microalgae. Most microalgae found in this study form large colonies (< 10 cells, or > 25 μm), which may protect them against invertebrate grazing. This findi...
Uploads
Papers by Jakub D Zarsky