Abstract
The characterization and modeling of polarized foregrounds has become a critical issue in the quest for primordial
B
-modes. A typical method to proceed is to factorize and parametrize the ...spectral properties of foregrounds and their scale dependence (i.e. assuming that foreground spectra are well described everywhere by their sky average). Since in reality foreground properties vary across the Galaxy, this assumption leads to inaccuracies in the model that manifest themselves as biases in the final cosmological parameters (in this case the tensor-to-scalar ratio
r
). This is particularly relevant for surveys over large fractions of the sky, such as the Simons Observatory (SO), where the spectra should be modeled over a distribution of parameter values. Here we propose a method based on the existing “moment expansion” approach to address this issue in a power-spectrum-based analysis that is directly applicable in ground-based multi-frequency data. Additionally, the method uses only a small set of parameters with simple physical interpretation, minimizing the impact of foreground uncertainties on the final
B
-mode constraints. We validate the method using SO-like simulated observations, recovering an unbiased estimate of the tensor-to-scalar ratio
r
with standard deviation σ(
r
) ≃ 0.003, compatible with official forecasts. When applying the method to the public BICEP2/
Keck
data, we find an upper bound
r
< 0.06 (95% C.L.), compatible with the result found by BICEP2/
Keck
when parametrizing spectral index variations through a scale-independent frequency decorrelation parameter. We also discuss the formal similarities between the power spectrum-based moment expansion and methods used in the analysis of CMB lensing.
Cryoconite holes, ponds full of melting water with sediment on the bottom, are hotspots of biodiversity on glacier surfaces and host dynamic micro-ecosystems. They have been extensively investigated ...in different areas of the world (e.g., the Arctic, Antarctic, Alps, and Himalaya), but so far no study has described the bacterial communities of the glaciers in the Andes, the world's longest mountain range. In this study, we describe the bacterial communities of three small (< 2 km
) high-elevation (< 4200 m a.s.l.) glaciers of the Central Andes (Iver, East Iver and Morado glaciers) and two large (> 85 km
) glaciers of the Patagonian Andes (Exploradores and Perito Moreno glaciers) whose ablation tongues reach low altitude (< 300 m a.s.l.). Results show that the bacterial communities were generally similar to those observed in the cryoconite holes of other continents, but with few cyanobacteria (0.5% of sequences). The most abundant orders were Betaproteobacteriales, Cytophagales, Chitinophagales, Acetobacterales, Frankiales, Armatimonadales, Sphingobacteriales, Rhizobiales, Bacteroidales, Sphingomonadales, and Micrococcales. The bacterial communities differed between glaciers and both water pH and O
concentration appeared to influence the bacterial community composition. This work thus provides the first description of the bacterial communities in cryoconite holes of South American glaciers.
In this study, the early ecological succession patterns of Forni Glacier (Ortles-Cevedale group, Italian Alps) forefield along an 18-year long chronosequence (with a temporal resolution of 1 year) ...has been reported. Bacterial and fungal community structures were inferred by high-throughput sequencing of 16S rRNA gene and ITS, respectively. In addition, the occurrence of both herbaceous and arboreous plants was also recorded at each plot. A significant decrease of alpha-diversity in more recently deglaciated areas was observed for both bacteria and plants. Time since deglaciation and pH affected the structure of both fungal and bacterial communities. Pioneer plants could be a major source of colonization for both bacterial and fungal communities. Consistently, some of the most abundant bacterial taxa and some of those significantly varying with pH along the chronosequence (Polaromonas, Granulicella, Thiobacillus, Acidiferrobacter) are known to be actively involved in rock-weathering processes due to their chemolithotrophic metabolism, thus suggesting that the early phase of the chronosequence could be mainly shaped by the biologically controlled bioavailability of metals and inorganic compounds. Fungal communities were dominated by ascomycetous filamentous fungi and basidiomycetous yeasts. Their role as cold-adapted organic matter decomposers, due to their heterotrophic metabolism, was suggested.
Cryoconite is rich in natural and artificial
radioactivity, but a discussion about its ability to accumulate
radionuclides is lacking. A characterization of cryoconite from two Alpine
glaciers is ...presented here. Results confirm that cryoconite is significantly
more radioactive than the matrices usually adopted for the environmental
monitoring of radioactivity, such as lichens and mosses, with activity
concentrations exceeding 10 000 Bq kg−1 for single radionuclides. This
makes cryoconite an ideal matrix to investigate the deposition and
occurrence of radioactive species in glacial environments. In addition,
cryoconite can be used to track environmental radioactivity sources. We have
exploited atomic and activity ratios of artificial radionuclides to identify
the sources of the anthropogenic radioactivity accumulated in our samples.
The signature of cryoconite from different Alpine glaciers is compatible
with the stratospheric global fallout and Chernobyl accident products.
Differences are found when considering other geographic contexts. A
comparison with data from literature shows that Alpine cryoconite is
strongly influenced by the Chernobyl fallout, while cryoconite from other
regions is more impacted by events such as nuclear test explosions and
satellite reentries. To explain the accumulation of radionuclides in
cryoconite, the glacial environment as a whole must be considered, and
particularly the interaction between ice, meltwater, cryoconite and
atmospheric deposition. We hypothesize that the impurities originally
preserved into ice and mobilized with meltwater during summer, including
radionuclides, are accumulated in cryoconite because of their affinity for
organic matter, which is abundant in cryoconite. In relation to these
processes, we have explored the possibility of exploiting radioactivity to date
cryoconite.
The observation of the polarised emission from the Cosmic Microwave Background (CMB) fromfuture ground-based and satellite-borne experiments holds the promise of indirectly detecting theelusive ...signal from primordial tensor fluctuations in the form of large-scale B-modepolarisation. Doing so, however, requires an accurate and robust separation of the signal frompolarised Galactic foregrounds. We present a component separation method for multi-frequency CMBobservations that combines some of the advantages of map-based and power-spectrum-basedtechniques, and which is direcly applicable to data in the presence of realistic foregrounds andinstrumental noise. We demonstrate that the method is able to reduce the contamination fromGalactic foregrounds below an equivalent tensor-to-scalar ratio rFG ≲ 5 × 10-4, as required for next-generation observatories, for a wide range offoreground models with varying degrees of complexity. This bias reduction is associated with amild ∼20–30% increase in the final statistical uncertainties, and holds for largesky areas, and for experiments targeting both the reionisation and recombination bumps in theB-mode power spectrum.
Biological processes on glacier surfaces affect glacier reflectance, influence surface energy budget and glacier response to climate warming, and determine glacier carbon exchange with the ...atmosphere. Currently, carbon balance of supraglacial environment is assessed as the balance between the activity of oxygenic phototrophs and the respiration rate of heterotrophic organisms. Here we present a metagenomic analysis of tiny wind-blown supraglacial sediment (cryoconite) from Baltoro (Pakistani Karakoram) and Forni (Italian Alps) glaciers, providing evidence for the occurrence in these environments of different and previously neglected metabolic pathways. Indeed, we observed high abundance of heterotrophic anoxygenic phototrophs, suggesting that light might directly supplement the energy demand of some bacterial strains allowing them to use as carbon source organic molecules, which otherwise would be respired. Furthermore, data suggest that CO
could be produced also by microbiologically mediated oxidation of CO, which may be produced by photodegradation of organic matter.
We here investigated the recent (1976–2014) evolution of the Ararat mountain glaciers, paradigmatic of the evolution of ice bodies in Western Asia and the Caucasus. We gathered ice cover maps, ...including debris cover from different sources, to depict glaciers’ extension, and its variation under recent climate patterns. We then gathered data of (daily/monthly) weather variables (temperature, precipitation, snow cover depth) from two local stations managed by Turkish State Meteorological Service, which we subsequently analyzed to assess the presence of significant trends. We used the recently developed, weather-driven glaciological model
Poly
-
Ice
, able to mimic distributed ice and snow melt, mass budget, and gravity-driven ice flow of glaciers, to reproduce recent evolution of the Ararat ice bodies. We found a measurable decrease of the area (− 2.38 km
2
, − 30% of the initial area, − 0.06 km
2
year
−1
) of the Ararat glaciers, including loss of ice under debris covered tongue (− 1.99 km
2
, − 70% of the initial area), driven by significantly increasing temperature especially in spring (+ 0.05 °C year
−1
). Using our Poly-Ice model, we could (i) mechanistically reproduce the response of the glaciers to the changing climate patterns, (ii) confirm faster downwasting ever since the 1990s under increasing temperature, and (iii) highlight decreased winter snow cover at thaw at the highest altitudes ever since the 1990s, further driving ice melt. Such physically based tool will further allow to project forward the dynamics of these glaciers under future climate. Our results are fully consistent with the present know how of glaciers’ retreat from Europe to Caucasus, and Central and Southern Asia, and contribute to the ongoing discussion about retreating glaciers worldwide.
Abstract
We present a demonstration of the in-flight polarization angle calibration for the JAXA/ISAS second strategic large class mission,
LiteBIRD
, and estimate its impact on the measurement of ...the tensor-to-scalar ratio parameter,
r
, using simulated data.
We generate a set of simulated sky maps with CMB and polarized foreground emission, and inject instrumental noise and polarization angle offsets to the 22 (partially overlapping)
LiteBIRD
frequency channels. Our in-flight angle calibration relies on nulling the EB cross correlation of the polarized signal in each channel. This calibration step has been carried out by two independent groups with a blind analysis, allowing an accuracy of the order of a few arc-minutes to be reached on the estimate of the angle offsets. Both the corrected and uncorrected multi-frequency maps are propagated through the foreground cleaning step, with the goal of computing clean CMB maps. We employ two component separation algorithms, the Bayesian-Separation of Components and Residuals Estimate Tool (
B-SeCRET
), and the Needlet Internal Linear Combination (
NILC
). We find that the recovered CMB maps obtained with algorithms that do not make any assumptions about the foreground properties, such as
NILC
, are only mildly affected by the angle miscalibration. However, polarization angle offsets strongly bias results obtained with the parametric fitting method. Once the miscalibration angles are corrected by EB nulling prior to the component separation, both component separation algorithms result in an unbiased estimation of the
r
parameter. While this work is motivated by the conceptual design study for
LiteBIRD
, its framework can be broadly applied to any CMB polarization experiment. In particular, the combination of simulation plus blind analysis provides a robust forecast by taking into account not only detector sensitivity but also systematic effects.
Modern parametric amplifiers are based on lithographically produced superconducting thin-film planar transmission line structures. These paramps rely on resonant structures with embedded nonlinear ...elements to stimulate intermodulation with a stronger pump tone that gives rise to signal gain when certain conditions are satisfied. Such paramps have not yet been realised in superconducting 3D waveguide resonators. Possible applications of these devices include detector systems that are based on 3D waveguide such as dark matter detectors and quantum computers. Reported here are the results of an investigation of a 30.64 GHz series circular waveguide resonance machined from bulk niobium showing parametric gain of up to 2 dB in the presence of a stronger pump tone 10 kHz above in frequency. The gain is largest on abrupt jumps of the transmission spectra of the resonance, which may be a result of weak-link formation on the superconducting surfaces.
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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