Jakub D Zarsky

<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

<p>Glaciers and ice sheets cover around 10% of the Earth’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<sup>3</sup> annually. There have been recent studies linking subglacial environments of the GrIS with methane (CH<sub>4</sub>) production and release, presenting a possible positive climate feedback. Previous work has linked organic carbon in subglacial environments with significant CH<sub>4</sub> 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<sub>4</sub> budget.</p><p>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<sub>4</sub> release from the GrIS, mainly because of the limited understanding of subglacial carbon cycling and the potential sources of CH<sub>4</sub> in these environments.  </p><p>We present the first data from two new, complimentary projects investigating CH<sub>4</sub> release from the GrIS margin, where we aim to quantify the production and release of CH<sub>4</sub> into the atmosphere from the GrIS. We have developed an ambitious temporal and spatial sampling regime to evaluate the CH<sub>4</sub> release along the western margin of the GrIS. We present the first radiocarbon (<sup>14</sup>C) dated CH<sub>4</sub> samples from Greenland, helping to shed light on the carbon cycling processes occurring under the ice sheet. We analyse a mixture of atmospheric CH<sub>4</sub> exported from subglacial ice caves and dissolved CH<sub>4</sub> from proglacial rivers draining subglacial portals to explore the age of subglacially sourced CH<sub>4</sub>.</p><p>We can combine the carbon age of exported CH<sub>4</sub> with microbial analysis and stable isotope data to improve our understanding of the environmental controls on and microbial sources of subglacial CH<sub>4</sub> production and export. Understanding the mechanisms behind subglacial CH<sub>4</sub> 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<sub>4</sub>, leading to a substantial, yet currently understudied climatic feedback.</p>

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 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...

 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 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 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, 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 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...

AimLarge number of indices for presence-absence data that compare two assemblages have been proposed or reinvented. Interpretation of these indices varies across the literature, despite efforts for clarification and unification. Most effort has focused on the mathematics behind the indices, their relationships with diversity, and between each other. At the same time, following issues have been largely overlooked: (i) inter-dependence of indices based on their informational value, (ii) overlap of the ecological phenomena that the indices aim to capture, (iii) requirement that a small re-arrangement of assemblages should only cause a small change in an index, and (iv) inferences from the indices about diversity patterns. Underappreciation of these issues has led to invention or reinvention of indices without increasing their information value. We offer a framework for pairwise diversity indices that accounts for these issues.MethodsWe present a framework that links different ecologica...

<p><strong>Figure 4.</strong> RDA triplot showing the effects of environmental variables (dashed arrows for quantitative and filled triangles for categories) on the abundance of 16S rRNA and <em>amoA</em> genes (solid arrows) in cryoconite holes on Aldegondabreen. Sites are marked by empty grey circles. Only significant factors (<em>p</em> < 0.01) are shown.</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

<p><strong>Figure 3.</strong> RDA biplot visualizing the effects of physical environmental variables (dashed arrows for quantitative and filled triangles for categories) on the chemistry (solid arrows) of cryoconite holes on Aldegondabreen. Only significant factors (<em>p</em> < 0.01) are shown.</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

<p><b>Table 4.</b>  Abundances of the 16S rRNA gene and bacterial and archaeal <em>amoA</em> genes (gene copies g<sup>−1</sup>) in cryoconite on Aldegondabreen (mean ± sd; <em>n</em> = 3). b.d. below detection limit. </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

For tens of millions of years (Ma), the terrestrial habitats of Snowball Earth during the Cryogenian period (between 720 to 635 Ma before present – Neoproterozoic Era) were possibly dominated by global snow and ice cover up to the equatorial sublimative desert. The most recent time-calibrated phylogenies calibrated not only on plants but on a comprehensive set of eukaryotes indicate that within the Streptophyta, multicellular charophytes (Phragmoplastophyta) evolved in Mesoproterozoic to early Neoproterozoic. At the same time, Cryogenian is the time of likely origin of the common ancestor of Zygnematophyceae and Embryophyta and later also of the Zygnematophyceae – Embryophyta split. This common ancestor is proposed to be called Anydrophyta; here, we use anydrophytes. Based on the combination of published phylogenomic studies and estimated diversification time comparisons, we deem highly likely that anydrophytes evolved in response to Cryogenian cooling. Also, later in the Cryogenian...

Microorganisms are flushed from the Greenland Ice Sheet (GrIS) where they may contribute towards the nutrient cycling and community compositions of downstream ecosystems. We investigate meltwater microbial assemblages as they exit the GrIS from a large outlet glacier, and as they enter a downstream river delta during the record melt year of 2012. Prokaryotic abundance, flux and community composition was studied, and factors affecting community structures were statistically considered. The mean concentration of cells exiting the ice sheet was 8.30 × 10(4) cells mL(-1) and we estimate that ∼1.02 × 10(21) cells were transported to the downstream fjord in 2012, equivalent to 30.95 Mg of carbon. Prokaryotic microbial assemblages were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Cell concentrations and community compositions were stable throughout the sample period, and were statistically similar at both sample sites. Based on our observations, we argue that the subglac...

Ice sheets are currently ignored in global methane budgets. They have been proposed to cap large reserves of methane that may contribute to a rise in atmospheric methane concentrations if released during periods of rapid ice retreat, but no data on the current methane footprint of ice sheets currently exist. Here we find that subglacially-produced methane is rapidly flushed to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland Ice Sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice sheet bed during the melt season. Pulses of high CH4(aq) concentrations coincided with supraglacially-forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season were indicative of subglacial methane reserves in excess of export, with an estimated 6.3 (2.4 – 11) tonnes of CH4(aq) laterally transported from the ice s...