Blooms of Zygnematophycean “glacier algae” lower the bare ice albedo of the Greenland Ice Sheet (GrIS), amplifying summer energy absorption at the ice surface and enhancing meltwater runoff from the ...largest cryospheric contributor to contemporary sea-level rise. Here, we provide a step change in current understanding of algal-driven ice sheet darkening through quantification of the photophysiological mechanisms that allow glacier algae to thrive on and darken the bare ice surface. Significant secondary phenolic pigmentation (11 times the cellular content of chlorophyll a) enables glacier algae to tolerate extreme irradiance (up to ∼4,000 μmol photons·m−2·s−1) while simultaneously repurposing captured ultraviolet and short-wave radiation for melt generation. Total cellular energy absorption is increased 50-fold by phenolic pigmentation, while glacier algal chloroplasts positioned beneath shading pigments remain low-light–adapted (Ek
∼46 μmol photons·m−2·s−1) and dependent upon typical nonphotochemical quenching mechanisms for photoregulation. On the GrIS, glacier algae direct only ∼1 to 2.4% of incident energy to photochemistry versus 48 to 65% to ice surface melting, contributing an additional ∼1.86 cm water equivalent surface melt per day in patches of high algal abundance (∼10⁴ cells·mL−1). At the regional scale, surface darkening is driven by the direct and indirect impacts of glacier algae on ice albedo, with a significant negative relationship between broadband albedo (Moderate Resolution Imaging Spectroradiometer MODIS) and glacier algal biomass (R² = 0.75, n = 149), indicating that up to 75% of the variability in albedo across the southwestern GrIS may be attributable to the presence of glacier algae.
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Historically, glaciers have been seen as pristine environments. However, recent research has shown that glaciers can accumulate and store contaminants over long timescales, through processes such as ...atmospheric deposition, sedimentation, glacial hydrology and mass movements. Studies have identified numerous anthropogenically derived contaminants within the global cryosphere, including the six we focus on here: fallout radionuclides; microplastics; persistent organic pollutants; potentially toxic elements; black carbon and nitrate-based contaminants. These contaminants are relatively well-studied in other environments; however, their dynamics and role in glaciated systems is still poorly understood. Therefore, it is important to assess and quantify contaminant levels within the cryosphere, so that current and future threats can be fully understood and mitigated. In this first progress report (Part I: Inputs and accumulation), we review the current state of knowledge of six of the most common anthropogenic contaminants found in the cryosphere, and consider their sources, transportation, accumulation and concentration within glacial systems. A second progress report (Part II: Release and downstream consequences) will outline how these contaminants leave glacial systems and the consequences that this release can have for communities and ecosystems reliant on glacial meltwater.
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Cryoconite holes, supraglacial depressions containing water and microbe-mineral aggregates, are known to be hotspots of microbial diversity on glacial surfaces. Cryoconite holes form in a variety of ...locations and conditions, which impacts both their structure and the community that inhabits them. Using high-throughput 16S and 18S rRNA gene sequencing, we have investigated the communities of a wide range of cryoconite holes from 15 locations across the Arctic and Antarctic. Around 24 bacterial and 11 eukaryotic first-rank phyla were observed in total. The various biotic niches (grazer, predator, photoautotroph, and chemotroph), are filled in every location. Significantly, there is a clear divide between the bacterial and microalgal communities of the Arctic and that of the Antarctic. We were able to determine the groups contributing to this difference and the family and genus level. Both polar regions contain a "core group" of bacteria that are present in the majority of cryoconite holes and each contribute >1% of total amplicon sequence variant (ASV) abundance. Whilst both groups contain Microbacteriaceae, the remaining members are specific to the core group of each polar region. Additionally, the microalgal communities of Arctic cryoconite holes are dominated by
whereas the Antarctic cryoconite holes are dominated by
. Therefore cryoconite holes may be a global feature of glacier landscapes, but they are inhabited by regionally distinct microbial communities. Our results are consistent with the notion that cryoconite microbiomes are adapted to differing conditions within the cryosphere.
Cryoconite is a sediment occurring on glacier surfaces worldwide which reduces ice albedo and concentrates glacier surface meltwater into small reservoirs called cryoconite holes. It consists of ...mineral and biogenic matter, including active microorganisms. This study presents an experimental insight into the influence of sediment oxygenation on the cryoconite ability to produce and decomposition of organic matter. Samples were collected from five glaciers in the Arctic and the European mainland. Cryoconite from three glaciers was incubated in stagnant and mechanically mixed conditions to imitate inter-hole water–sediment mixing by meltwater occurring on glaciers in Northern Hemisphere, and its effect on oxygen profiles and organic matter content. Moreover, we investigated short-term changes of oxygen conditions in cryoconite from four glaciers in illuminated and dark conditions. An anaerobic zone was present or approaching zero oxygen in all illuminated cryoconite samples, varying in depth depending on the origin of cryoconite: from 1500 µm from Steindalsbreen (Scandinavian Peninsula) and Forni Glacier (The Alps) to 3100 µm from Russell Glacier and Longyearbreen (Arctic) after incubation. Organic matter content varied between glaciers from 6.11% on Longyearbreen to 16.36% on Russell Glacier. The mixed sediment from the Forni Glacier had less organic matter than stagnant, the sediment from Longyearbreen followed this trend, but the difference was not statistically significant, while the sediment from Ebenferner did not differ between groups. Our results have implications for the understanding of biogeochemical processes on glacier surfaces, the adaptation of organisms to changing physical conditions due to abrupt sediment mixing, but also on the estimation of productivity of supraglacial systems.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Cryoconite is a mixture of mineral and organic material covering glacial ice, playing important roles in biogeochemical cycles and lowering the albedo of a glacier surface. Understanding the ...differences in structure of cryoconite across the globe can be important in recognizing past and future changes in supraglacial environments and ice-organisms-minerals interactions. Despite the worldwide distribution and over a century of studies, the basic characteristics of cryoconite, including its forms and geochemistry, remain poorly studied. The major purpose of our study is the presentation and description of morphological diversity, chemical and photoautotrophs composition, and organic matter content of cryoconite sampled from 33 polar and mountain glaciers around the globe. Observations revealed that cryoconite is represented by various morphologies including loose and granular forms. Granular cryoconite includes smooth, rounded, or irregularly shaped forms; with some having their surfaces covered by cyanobacteria filaments. The occurrence of granules increased with the organic matter content in cryoconite. Moreover, a major driver of cryoconite colouring was the concentration of organic matter and its interplay with minerals. The structure of cyanobacteria and algae communities in cryoconite differs between glaciers, but representatives of cyanobacteria families Pseudanabaenaceae and Phormidiaceae, and algae families Mesotaeniaceae and Ulotrichaceae were the most common. The most of detected cyanobacterial taxa are known to produce polymeric substances (EPS) that may cement granules. Organic matter content in cryoconite varied between glaciers, ranging from 1% to 38%. The geochemistry of all the investigated samples reflected local sediment sources, except of highly concentrated Pb and Hg in cryoconite collected from European glaciers near industrialized regions, corroborating cryoconite as element-specific collector and potential environmental indicator of anthropogenic activity. Our work supports a notion that cryoconite may be more than just simple sediment and instead exhibits complex structure with relevance for biodiversity and the functioning of glacial ecosystems.
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•The morphology of cryoconite varies greatly between regions.•Cryoconite consists of loose mineral material or various types of granules.•Colour of cryoconite depends on organic matter content and its interplay with minerals.•Cryoconite is a complex structure providing various ecological niches for glacial microbes.
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Cryoconite holes are miniature freshwater aquatic ecosystems that harbor a relatively diverse microbial community. This microbial community can withstand the extreme conditions of the supraglacial ...environment, including fluctuating temperatures, extreme and varying geochemical conditions and limited nutrients. We analyzed the physiological capabilities of microbial isolates from cryoconite holes from Antarctica, Greenland, and Svalbard in selected environmental conditions: extreme pH, salinity, freeze-thaw and limited carbon sources, to identify their physiological limits. The results suggest that heterotrophic microorganisms in cryoconite holes are well adapted to fast-changing environmental conditions, by surviving multiple freeze-thaw cycles, a wide range of salinity and pH conditions and scavenging a variety of organic substrates. Under oxic and anoxic conditions, the communities grew well in temperatures up to 30°C, although in anoxic conditions the community was more successful at colder temperatures (0.2°C). The most abundant cultivable microorganisms were facultative anaerobic bacteria and yeasts. They grew in salinities up to 10% and in pH ranging from 4 to 10.5 (Antarctica), 2.5 to 10 (Svalbard), and 3 to 10 (Greenland). Their growth was sustained on at least 58 single carbon sources and there was no decrease in viability for some isolates after up to 100 consecutive freeze-thaw cycles. The elevated viability of the anaerobic community in the lowest temperatures indicates they might be key players in winter conditions or in early melt seasons, when the oxygen is potentially depleted due to limited flow of meltwater. Consequently, facultative anaerobic heterotrophs are likely important players in the reactivation of the community after the polar night. This detailed physiological investigation shows that despite inhabiting a freshwater environment, cryoconite microorganisms are able to withstand conditions not typically encountered in freshwater environments (namely high salinities or extreme pH), making them physiologically more similar to arid soil communities. The results also point to a possible resilience of the most abundant microorganisms of cryoconite holes in the face of rapid change regardless of the location.
Anthropogenic contamination has been detected in glacial and proglacial environments around the globe. Through mechanisms of secondary release, these contaminants are finding their way into glacial ...hydrological systems and downstream environments, with potential to impact hundreds of millions of people who rely on glacial meltwater for water, food and energy security worldwide. The first part of our progress report outlined the sources and accumulation mechanisms of contaminants in glacial environments (Part I: Inputs and accumulation). Here we assess processes of contaminant release, pathways to downstream environments, and socio-environmental consequences. We reflect on the potential impacts these contaminants could have for human, ecosystem, and environmental health, as well as framing glacial contaminants within the context of the water-food-energy nexus. Improved understanding of these processes and impacts, while crucially embedding local knowledge, will help to develop key policy and mitigation strategies to address future risk of contaminant release from glaciers.
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Glaciers and ice sheets host abundant and dynamic communities of
microorganisms on the ice surface (supraglacial environments). Recently, it
has been shown that Streptophyte glacier algae blooming on ...the surface ice
of the south-western coast of the Greenland Ice Sheet are a significant
contributor to the 15-year marked decrease in albedo. Currently, little is
known about the constraints, such as nutrient availability, on this
large-scale algal bloom. In this study, we investigate the relative
abundances of dissolved inorganic and dissolved organic macronutrients (N
and P) in these darkening surface ice environments. Three distinct ice
surfaces, with low, medium and high visible impurity loadings, supraglacial
stream water and cryoconite hole water, were sampled. Our results show a
clear dominance of the organic phase in all ice surface samples containing
low, medium and high visible impurity loadings, with 93 % of the total
dissolved nitrogen and 67 % of the total dissolved phosphorus in the
organic phase. Mean concentrations in low, medium and high visible impurity
surface ice environments are 0.91, 0.62 and 1.0 µM for dissolved inorganic nitrogen (DIN), 5.1, 11 and 14 µM for dissolved organic nitrogen (DON), 0.03, 0.07 and 0.05 µM for dissolved inorganic phosphorus (DIP) and 0.10, 0.15 and 0.12 µM for dissolved organic phosphorus
(DOP), respectively. DON concentrations in all three surface ice samples are
significantly higher than DON concentrations in supraglacial streams and
cryoconite hole water (0 and 0.7 µM, respectively). DOP
concentrations are higher in all three surface ice samples compared to
supraglacial streams and cryoconite hole water (0.07 µM for both).
Dissolved organic carbon (DOC) concentrations increase with the amount of
visible impurities present (low: 83 µM, medium: 173 µM and
high: 242 µM) and are elevated compared to supraglacial streams and
cryoconite hole water (30 and 50 µM, respectively). We
speculate that the architecture of the weathering crust, which impacts on
water flow paths and storage in the melting surface ice and/or the
production of extracellular polymeric substances (EPS), containing both N
and P in conjunction with C, is responsible for the temporary retention of
DON and DOP in the melting surface ice. The unusual presence of measurable DIP
and DIN, principally as NH4+, in the melting surface ice
environments suggests that factors other than macronutrient limitation are
controlling the extent and magnitude of the glacier algae.
•SAPS1, a regulatory subunit of the protein phosphatase 6 has been deleted in mouse.•SAPS1 null mice and cells do not show any gross defect in growth and development.•SAPS1 null mice and cells show ...defect in DNA repair and are sensitive to DNA damaging agents.
Cellular responses to DNA damage include activation of DNA-dependent protein kinase (DNA-PK) through, among others, the serine/threonine protein phosphatase 6 (PP6). We previously showed that recognition of DNA-PKcs is mediated by the SAPS1 PP6 regulatory subunit. Here, we report and characterize a SAPS1 null mouse and investigate the effects of deletion on DNA damage signaling and repair. Strikingly, neither SAPS1-null animals nor cells derived from them show gross defects, unless subjected to DNA damage by radiation or chemical agents. The overall survival of SAPS1-null animals following whole body irradiation is significantly shortened as compared to wild-type mice, and the clonogenic survival of null cells subjected to ionizing radiation is reduced. The dephosphorylation of DNA damage/repair markers, such as γH2AX, p53 and Kap1, is diminished in SAPS1-null cells as compared to wild-type controls. Our results demonstrate that loss of SAPS1 confers sensitivity to DNA damage and confirms previously reported cellular phenotypes of SAPS1 knock-down in human glioma cells. The results support a role for PP6 regulatory subunit SAPS1 in DNA damage responses, and offer a novel target for sensitization to enhance current tumor therapies, with a potential for limited deleterious side effects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microorganisms play a significant role in changing the physical properties of the surface of the Greenland Ice Sheet. Cryoconite holes are a hotspot for this microbial activity, yet little is known ...about the REDOX conditions that develop within them. In this study, we used oxygen microelectrodes and microoptodes to measure for anoxic conditions at the microscale, for the first time revealing a potential niche for anaerobic microorganisms and anaerobic processes. The development of an anoxic zone 2 mm deep within a 6 mm-thick layer of cryoconite sediment was observed within an hour of disturbance, showing rapid acclimation to changing physical conditions. Long-term (half year) incubations of cryoconite material showed a peak of oxygen production and consumption after forty days and reached a low-activity, steady state by day 116, with a persisting anoxic zone beginning between 2 mm and 4 mm deep. Anaerobic microorganisms, which have received little attention to date, should therefore be considered an important component of the cryoconite ecosystem. We discuss the possible dynamics of oxygen concentrations in the supraglacial system and infer that anoxic zones are an important factor in the development of cryoconite sediment communities.
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