Glacier algae: a dark past and a darker future

“Glacier algae” grow on melting glacier and ice sheet surfaces across the cryosphere, causing the ice to absorb more solar energy and consequently melt faster, while also turning over carbon and nutrients. This makes glacier algal assemblages, which are typically dominated by just three main species, a potentially important yet under-researched component of the global biosphere, carbon, and water cycles. This review synthesizes current knowledge on glacier algae phylogenetics, physiology, and ecology. We discuss their significance for the evolution of early land plants and highlight their impacts on the physical and chemical supraglacial environment including their role as drivers of positive feedbacks to climate warming, thereby demonstrating their influence on Earth’s past and future. Four complementary research priorities are identified, which will facilitate broad advances in glacier algae research, including establishment of reliable culture collections, sequencing of glacier algae genomes, development of diagnostic biosignatures for remote sensing, and improved predictive modeling of glacier algae biological-albedo effects

Meltwater export of prokaryotic cells from the Greenland ice sheet

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 × 104 cells mL−1 and we estimate that ∼1.02 × 1021 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 subglacial environment is the primary source of the river-transported microbiota, and that cell export from the GrIS is dependent on discharge. We hypothesise that the release of subglacial microbiota to downstream ecosystems will increase as freshwater flux from the GrIS rises in a warming world

Greenland melt drives continuous export of methane from the ice-sheet bed

Ice sheets are currently ignored in global methane budgets1,2. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid ice retreat3,4, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven 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) concentration coincide 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 are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation5 to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once runoff reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers6. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth’s methane budget

Potential for Microbial Nitrogen Cycling in the Supraglacial Environment of the High Arctic

Unser Verständnis vom Nährstoffzyklus des Ökosystems der Hohen Arktis ist essentiell für die Verfolgung vom Schicksal der atmosphärischen Stickstoffdepositionen in diesem höchst sensitiven Milieu. Diese repräsentieren - oft in höchst konzentrierter Form - einen Input von reaktiven Formen von Stickstoff und finden sich entlang der Gletscherzuflussgebiete, die durch ein Ökosystem mit extremen Lebensbedingungen wie Nährstofflimitierung charakterisiert und mikrobiell dominiert sind. Nach einer Übersicht (Kapitel 1) über biologische Prozesse auf Gletscheroberflächenzeigt die vorliegende Arbeit einen Versuch einer Synthese zwischen biotischen und abiotischen Prozessen im Kontext mit dem N-Kreislauf dar. i) Darstellung über das Ausmaß der proteosynthetischen Aktivität (ein Stickstoff verbrauchender Prozess), der Mikroben mit Hilfe der Messung von von [3H]Leucin-Inkorporation im Laufe von in situ Inkubationen von Proben verschiedener Habitate der schmelzenden Schneedecke (Kapitel 2 und 4). ii) Untersuchung der mikrobiellen Diversität in der schmelzenden Schneedecke und Kryokonit-Sediment auf der Gletscheroberfläche in der Ablationszone mit Hilfe von modernen analytischen Methoden (qPCR, 454 sequencing). Wir fokussieren auf mikrobielle Gruppen, welche für die Ammonium-Oxidation charakteristisch sind (incl. amoA funktionellem Gen). Weiters werden erstmals Ammonium-oxidierende Archaeen für supraglaziale Habitate nachgewisen (Kapitel 3 und 5). Das letzte Kapitel (Conclusions and Perspective) hebt den Kontext und die Perspektive weiterer Forschungen hervor, welche in den partiellen Zusammenfassungen der einzelnen Kapitel nicht behandelt werden konnten.Our understanding of nutrient cycling in the High Arctic ecosystem is essential for tracking the fate of atmospheric nitrogen depositions in this highly sensitive environment. The atmospheric nitrogen deposition represents - often a highly concentrated - flux of its reactive forms and it takes a journey trough glacial catchments characteristic by an extreme, microbial-dominated and nutrient limited ecosystem. This work represents an attempt to push our knowledge a small step further by i) asking questions about microbial presence, transport and magnitude of proteosynthetic activity (nitrogen consuming processs) by assessing the [3H]leucine incorporation rate by in situ incubation of samples from different habitats in the melting snow pack (second and fourth chapter). ii) By investigation of microbial diversity in melting snow pack and in the cryoconite sediment on the glacial surface in the ablation zones using modern analytical methods (qPCR, 454 sequencing). We focused on the presence of microbial groups characteristic by ammonium-oxidation (incl. the functional gene amoA) and we report ammonium-oxidizing archaea for the first time in supraglacial environment (third and fifth chapter). The first chapter is a review paper presenting the topic of biological processes on glacier and ice sheet surfaces in a condensed form. The last chapter (Conclusions and perspective) points out the context and the perspectives of further research, which were not covered in the conclusions of particular chapters.von Jakub D. ZarskyEnth. u.a. 5 Veröff. d. Verf. aus den Jahren 2012 - 2013 . - Zsfassung in dt. SpracheInnsbruck, Univ., Diss., 2014OeBB(VLID)16756

Supraglacial bacterial community structures vary across the Greenland ice sheet

The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km2) 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

Microbial abundance in surface ice on the Greenland Ice Sheet

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, 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) 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 ca 2 x 10^3 to ca 2 x 10^6 cells/ml while dust concentrations ranged from 0.01 to 2 mg/ml. 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 Greenland Ice Sheet

Silicon isotopes in Arctic and sub-Arctic glacial meltwaters: the role of subglacial weathering in the silicon cycle

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 as dissolvable amorphous silica (ASi). Silicon is a key nutrient in promoting marine primary productivity, contributing to atmospheric CO2 removal. We present the current understanding of Si cycling in glacial systems, focusing on the Si isotope (δ30Si) composition of glacial meltwaters. We combine existing glacial δ30Si data with new measurements from 20 sub-Arctic glaciers, showing that glacial meltwaters consistently export isotopically light DSi compared with non-glacial rivers (+0.16‰ versus +1.38‰). Glacial δ30SiASi composition ranges from −0.05‰ to −0.86‰ but exhibits low seasonal variability. Silicon fluxes and δ30Si 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

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

<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

(A) Aldegondabreen in Grønfjorden, the study site in Svalbard

<p><strong>Figure 1.</strong> (A) Aldegondabreen in Grønfjorden, the study site in Svalbard. (B) Location of the sampling sites on the surface of Aldegondabreen. Transects (A)–(B) are numbered from the lowest point upstream. In transect (B) only the point B2 was analysed. (C) Northern margin of Aldegondabreen with sampling points A3 and A4 as seen from point A2 with marked areas of bird nesting activity and occurrence of large cryoconite granules. White circles indicate the area in the slopes of Productustoppen (527 m) with nesting seabirds. (D) Large cryoconite aggregate in detail with visible cyanobacterial mat on its surface. (E) View on the glacier surface at transect (A). The scale was derived from an 3 m long avalanche probe with cm scale. The probe is visible in the lower right part of the shot. The cryoconite aggregates cover the surface without producing deep melt ponds due to prevailing effect of conductive heat flux. (F) Large cryoconite sediment aggregates at point A2.</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