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The article discusses the use of tritium (H-3) and cesium (Cs-137) as temporal markers in ice cores extracted from temperate glaciers. We present a complete tritium profile for a 46 m ice core drilled from the Adamello Glacier, a temperate glacier in the Italian Alps, and compare it to the Cs-137 profile from the same ice core. Our analysis reveals tritium contamination between 19 and 32 m of depth, which can be attributed to the global radioactive fallout caused by atmospheric nuclear-bomb testing that took place in the 1950s and 1960s. Results show that the radioactive peak associated with 1963 does not occur at the same depth for both H-3 and Cs-137; instead, the tritium peak is 1.5 m above the cesium one. Our hypothesis is that this misalignment is caused by meltwater-induced post-depositional processes that affect Cs-137, which is more sensitive to percolation than H-3. The total inventory of Cs-137 in this ice core is also among the lowest ever reported, providing additional evidence that the presence of meltwater has affected the distribution of this radionuclide within the ice. In contrast, the total tritium inventory is comparable to what is reported in the literature, making it a more reliable temporal marker for temperate glaciers.

Paleoclimate and paleoenvironmental stratigraphic reconstructions from temperate glaciers are hindered by surface melting and ice metamorphism, which cause mobilization and concentration of impurities, as well as their interaction through englacial reactions. Despite meltwater intrusions, other impurities such as pollen grains and other palynomorphs remain to their original depth of deposition thanks to their large grain size. Temperate glaciers close to vegetated areas, therefore, can include palynomorphs of different types that i) can be reliable annual markers for ice-core dating and, ii) allow reconstructing paleoenvironmental changes through time. The Adamello Glacier (Central Alps, Italy) is a temperate glacier that extends over ca 14.35 km2 (2020) at elevations ranging between 2560 and 3420 m a.s.l. In the framework of the CLIMADA Project, a 224 m long ice core (ADA 270) was recovered in 2021 from Pian di Neve, the summit plateau at about 3200 m a.s.l. in the accumulation area of the glacier. Preliminary estimates date the surface ice of the glacier to the 1980s while the bottom of the core might be Medieval in age. Radionuclide-based dating (3H, 14C, 137Cs, 210Pb) is in progress. The multiproxy approach adopted in this study includes black carbon, dust grain size and mineralogy, oxygen and hydrogen stable isotopes and palynomorphs, these last being the main object of this work. Given the site location, the palaeoecological signal is believed to be of regional significance. Despite the stratigraphy may not be preserved for some soluble chemical species, the core contains a high variety of palynomorphs, which allow the reconstruction of palaeoenvironmental and paleoclimatic variations at subannual resolution. The mean ice accumulation rate is about 0.9 m w.eq. yr-1. Consequently, the mean sampling resolution adopted for the palynomorph study is 0.1 m, increased to 0.01 m in specific intervals. Palynomorphs are mainly found in layers representing the spring-sum

During the East Antarctic International Ice Sheet Traverse (Eaiist, december 2019), in an unexplored part of the East Antarctic Plateau, snow samples were collected to expand our knowledge of the latitudinal variability of iodine, bromine and sodium as well as their relation in connection with emission processes and photochemical activation in this unexplored area. A total of 32 surface (0–5 cm) and 32 bulk (average of 1 m depth) samples were taken and analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Our results show that there is no relevant latitudinal trend for bromine and sodium. For bromine they also show that it has no significant post-depositional mechanisms while its inland surface snow concentration is influenced by spring coastal bromine explosions. Iodine concentrations are several orders of magnitude lower than bromine and sodium and they show a decreasing trend in the surface samples concentration moving southward. This suggests that other processes affect its accumulation in surface snow, probably related to the radial reduction in the ozone layer moving towards central Antarctica. Even though all iodine, bromine and sodium present similar long-range transport from the dominant coastal Antarctic sources, the annual seasonal cycle of the ozone hole over Antarctica increases the amount of UV radiation (in the 280–320 nm range) reaching the surface, thereby affecting the surface snow photoactivation of iodine. A comparison between the bulk and surface samples supports the conclusion that iodine undergoes spring and summer snow recycling that increases its atmospheric lifetime, while it tends to accumulate during the winter months when photochemistry ceases.

Mineral dust is a natural tracer of atmospheric composition and climate variability. Yet, there is still much to be known about the Southern Hemisphere dust cycle. Major efforts have attempted to solve the puzzle of the origin of the potential source areas contributing dust to the Southern Ocean and East Antarctica. Here we present a comprehensive geochemical characterization of a source area, whose role as a dust supplier to high latitude environments has significantly been underestimated. Sediments collected within the major dust-producing areas along the Namibian coast in Southern Africa (Kuiseb, Omaruru and Huab river catchments and the Namib Sand Sea region), were analyzed for radiogenic isotope ratios and rare earth element concentrations. We find that during warm periods, the Southern African dust signature can be found in archives of the Southern Hemisphere, especially in the Atlantic sector of the Southern Ocean and peripheral areas of the East Antarctic plateau.

Paleoclimatic information recorded in polar and mountain glaciers are very important to study climate and environmental changes, telling a story about the ancient past and the ongoing cryosphere response to the anthropogenic impact. In this contest, a new high spatial resolution ice-core analysis has been done using a hyperspectral system, which allows to detect ice characteristics related to paleoclimatic information in a new non destructive way. This improves the accuracy of measurements and the preservation of samples. The hyperspectral analysis has been applied on sections from the ADA270 ice core project, drilled in 2021 at the Adamello-Mandrone glacial group (Pian di Neve, Eastern Alps, Italy). The optical method acquires reflectance images collecting spectral radiance in 840 bands in visible and NIR wavelengths (400-1000 nm). Different optical descriptors have been computed from all reflectance spectra to measure variations due to ice features and impurities encloses in ice layers. In particular, we considered the surface albedo and two spectral indices: Snow Darkening Index (SDI) and Impurity Index (II). From such descriptors continuous records along the core, in particular Albedo and SDI, samples are accurately selected and melted to make a discrete analysis with a Coulter Counter Beckman Multisizer 4e to make a calibration. Analyzed features are ice lenses, visible air bubbles, medium supposed dust concentration and high content of visible materials. The discrete data have been matched with SDI values for all analyzed sections to apply a regression model. A calibrated curve for impurities concentration has been created, providing a very important tool to not systematically apply destructive measurements in all ice-core sections. For a depth ranging from 14 m to around 35 m, many high concentration peaks (to a maximum of 30-35 ppm) have been identified and associated to visible impurities layers. The rest of the curve, highlights concentrations lower than 5

Le superfici ghiacciate del pianeta sono un archivio privilegiato di informazioni sulla storia climatica della Terra. La loro capacità di riflettere la radiazione solare (definita Albedo) è fortemente influenzata dalla deposizione di polveri minerali provenienti da diverse sorgenti, con un conseguente impatto sul budget energetico del pianeta e sulla qualità del segnale preservato nel ghiaccio. Le polveri minerali (dette dust), una volta depositate sui ghiacciai, causano l’assorbimento di maggiori porzioni della radiazione solare incidente in funzione della concentrazione, della composizione mineralogica e delle dimensioni delle particelle che le compongono. Il ghiacciaio dell’Adamello, il più profondo ed esteso delle Alpi italiane, è stato scelto come sito del progtto di ricerca ClimADA, che mira a ricostruire la storia climatica dell’arco alpino negli ultimi anni. Dal ghiacciaio è stata estratta nell’aprile 2021, nell’ambito del progetto ClimADA, una carota di ghiaccio di 224m, trasportata per la conservazione e l’analisi presso l’EuroCold Lab. (Università Milano-Bicocca), un’infrastruttura di ricerca di importanza internazionale per lo studio delle carote di ghiaccio. Per estrarre le informazioni climatiche garantendo la preservazione dell’archivio di ghiaccio, è stato utilizzato lo strumento HyIce sviluppato all’interno del DISAT e che utilizza la tecnica iperspettrale per generare immagini ad alta risoluzione in modo non distruttivo, producendo alcuni descrittori ottici come Albedo, Snow Darkening Index (SDI) e Impurity Index. Questa tecnica è in grado di descrivere rispettivamente la radiazione luminosa riflessa, l’annerimento e la presenza di impurità sulle superfici composte da ghiaccio come i ghiacciai e le coperture nevose. Ogni immagine è costruita da una matrice di riflettanza, proprietà fisica che descrive la quantità di radiazione luminosa riflessa in relazione al fascio incidente. I record così estratti per l’intera carota di ghiaccio co

Ice-covered surfaces of the planet are a pristine glimpse on the climate history of the Earth. Their capability to reflect the solar radiation affects the energy budget through time, so that paleoclimatic information recorded in polar and mountain glaciers tell a story about climate and environmental changes. Climate variations are a glaring reality due to a progressive climate warming that has been observed since the 1950s. The latest 2022 IPCC report [1], highlights the worrying state of the entire cryosphere health. Mid-latitude glaciers, e.g., are highly sensitive to the current atmospheric warming, which is seriously compromising the quality of the signal preserved in the ice. Mineral dust aerosol in atmosphere can alter the Earth’s energy budget interacting with the solar electromagnetic radiation. The dust settled on glaciers surfaces varies the ice capability to reflect the incident radiation, so that a major portion of it is absorbed as a function of Light Absorbing Impurity (LAI) concentration, mineralogical composition, LAI shapes etc. Depending on formation sites different minerals have different optical properties, affecting cryosphere mechanisms in a way that has to be further investigated. Ice core studies from mid-latitude mountain glaciers are essential to infer recent climate variability and anthropogenic impact on a regional scale. In the scientific literature, various imaging non-destructive systems extract e.g. information from visual stratigraphy of ice cores [2]. Advanced techniques can further be developed to improve the accuracy of ice cores measurements, pursuing the preservation of such precious achieves. The aim of this work is to apply different approaches to improve the understanding and climate simulation models regarding ice optical properties and feedback mechanisms, focusing on mineral dust and ice internal features. First, a non destructive system based on a hyperspectral imaging sensor is used to analyze optical properties of ice

Mineral dust aerosol plays an important role in climate and biogeochemical processes by providing nutrients to marine and terrestrial ecosystems and by influencing the radiation balance of the atmosphere. In turn, mineral dust responds to natural and anthropogenic alterations of land cover and land use resulting from several environmental changes that occurred on different timescales. Contamination by aerosols is a very tangible threat to the cryosphere in the European Alps due to its proximity to highly urbanized areas, cultivated landscapes, and the largest hot desert in the world. We recently developed and assembled a continuous flow analysis system for studying the solid content of ice cores with a high time resolution, focusing on optical characterization methods based on light scattering. The line is designed to provide an integrated measurement of dust particles with Single-Particle Extinction and Scattering (SPES), digital holography, and an optical particle sizer (Abakus). Many of the particles found in ice are efficient scatterers and absorbers close to the size range of the visible light wavelength. We report some preliminary results from ice cores drilled during the ADA270 project, aiming at an in-depth characterization of the samples that provide essential information on the fast climate evolution, which is causing a severe degeneration of glaciers, among other consequences.

Insoluble particles in ice cores record signatures of past climate parameters like vegetation dynamics, volcanic activity, and aridity. For some of them, the analytical detection relies on intensive bench microscopy investigation and requires dedicated sample preparation steps. Both are laborious, require in-depth knowledge, and often restrict sampling strategies. To help overcome these limitations, we present a framework based on flow imaging microscopy coupled to a deep neural network for autonomous image classification of ice core particles. We train the network to classify seven commonly found classes, namely mineral dust, felsic and mafic (basaltic) volcanic ash grains (tephra), three species of pollen (Corylus avellana, Quercus robur, Quercus suber), and contamination particles that may be introduced onto the ice core surface during core handling operations. The trained network achieves 96.8ĝ€ ̄% classification accuracy at test time. We present the system's potential and its limitations with respect to the detection of mineral dust, pollen grains, and tephra shards, using both controlled materials and real ice core samples. The methodology requires little sample material, is non-destructive, fully reproducible, and does not require any sample preparation procedures. The presented framework can bolster research in the field by cutting down processing time, supporting human-operated microscopy, and further unlocking the paleoclimate potential of ice core records by providing the opportunity to identify an array of ice core particles. Suggestions for an improved system to be deployed within a continuous flow analysis workflow are also presented.

During the East Antarctic International Ice Sheet Traverse (Eaiist, december 2019), in an unexplored part of the East Antarctic Plateau, snow samples were collected to expand our knowledge of the latitudinal variability of iodine, bromine and sodium as well as their relation in connection with emission processes and photochemical activation in this unexplored area. A total of 32 surface (0-5 cm) and 32 bulk (average of 1 m depth) samples were taken and analysed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Our results show that there is no relevant latitudinal trend for bromine and sodium. For bromine they also show that it has no significant post-depositional mechanisms while its inland surface snow concentration is influenced by spring coastal bromine explosions. Iodine concentrations are several orders of magnitude lower than bromine and sodium and they show a decreasing trend in the surface samples concentration moving southward. This suggests that other processes affect its accumulation in surface snow, probably related to the radial reduction in the ozone layer moving towards central Antarctica. Even though all iodine, bromine and sodium present similar long-range transport from the dominant coastal Antarctic sources, the annual seasonal cycle of the ozone hole over Antarctica increases the amount of UV radiation (in the 280-320 nm range) reaching the surface, thereby affecting the surface snow photoactivation of iodine. A comparison between the bulk and surface samples supports the conclusion that iodine undergoes spring and summer snow recycling that increases its atmospheric lifetime, while it tends to accumulate during the winter months when photochemistry ceases.

Thanks to its insolubility, mineral dust is considered a stable proxy in polar ice cores. With this study we show that the Talos Dome ice core (TALDICE, Ross Sea sector of East Antarctica) displays evident and progressive signs of post-depositional processes affecting the mineral dust record below 1000g m deep. We apply a suite of established and cutting-edge techniques to investigate the properties of dust in TALDICE, ranging from concentration and grain size to elemental composition and Fe mineralogy. Results show that through acidic/oxidative weathering, the conditions of deep ice at Talos Dome promote the dissolution of specific minerals and the englacial formation of others, affecting primitive dust features. The expulsion of acidic atmospheric species from ice grains and their concentration in localized environments is likely the main process responsible for englacial reactions. Deep ice can be seen as a "geochemical reactor"capable of fostering complex reactions which involve both soluble and insoluble impurities. Fe-bearing minerals can efficiently help in exploring such transformations.

A deeper understanding of past atmospheric circulation variability in the Central Andes is a high-priority topic in paleoclimatology mainly because of the necessity to validate climate models used to predict future precipitation trends and to develop mitigation and/or adaptation strategies for future climate change scenarios in this region.Within this context, we here investigate an 18-year firn core drilled at Nevado Illimani in order to interpret its mineral dust record in relation to seasonal processes, in particular atmospheric circulation and deep convection. The core was dated by annual layer counting based on seasonal oscillations of dust, calcium, and stable isotopes. Geochemical and mineralogical data show that dust is regionally sourced in winter and summer. During austral summer (wet season), an increase in the relative proportion of giant dust particles (20 um) is observed, in association with oscillations of stable isotope records (D, 18O). It seems that at Nevado Illimani both the deposition of dust and the isotopic signature of precipitation are influenced by atmospheric deep convection, which is also related to the total amount of precipitation in the area. This hypothesis is corroborated by regional meteorological data. The interpretation of giant particle and stable isotope records suggests that downdrafts due to convective activity promote turbulent conditions capable of suspending giant particles in the vicinity of Nevado Illimani. Giant particles and stable isotopes, when considered together, can be therefore used as a new proxy for obtaining information about deep convective activity in the past.

There is much information to be derived from the airborne dust that can be found in ice cores, especially about the aerosol composition and sources, including the characteristics of the atmosphere of several thousands of years ago. There is, in fact, much still to learn about both the data that can be retrieved and how to interpret them with appropriate models. One of the most striking aspects of these tiny particles is the effect their shape alone has on their scattering and absorption properties, which translate into a contribution to the Earth radiative transfer, especially at the wavelength scale. We show that aggregates of several particles behave differently from compact particles, and non-isometric compact particles can be clearly distinguished from isometric particles as their non-sphericity increases. We report the advances in this direction based on light scattering measurements on the dust content of ice cores drilled from Dome C and Dome B in Antarctica as part of the EPICA project, and provide a physical interpretation in terms of the known models in the field of light scattering by small particles.

During the last glaciation the Eurasian continent was impacted by the global reorganization of atmospheric circulation caused by North Atlantic events, through changes in moisture storm tracks modulated by orography. Our research explores the linkages between climate evolution in the North Atlantic and in the Alps between 30.6 and 12.5 ka, This period, centered on the Last Glacial Maximum, experienced the most recent phase of maximum global ice volume, corresponding to a millennia-long phase of sea-level lowstand, minima in reconstructed sea surface temperatures and isotopic values from polar ice. We present a high-resolution multiproxy record from Lake Fimon at the southern Alpine foothills, where a larch forest-steppe persisted throughout the coldest spells. We analyse the fine climate structure of the MIS 3–2 transition, of the Alpine Last Glacial Maximum stepped by HS2, and provide an unprecedented fine resolution and accurate 14C dating of the Last Glacial Maximum and the early Alpine Lateglacial. We reconstructed quantitative climate parameters based on sensitive pollen descriptors, and derived co-registered sedimentary proxies for dust flux. Reconstructed series suggest that extreme continental spells in the Alps and cold boreal winters match the timing of Heinrich Stadials 2 and 1, episodes of iceberg discharge and release of rock fragments (Ice Rafted Debris) in the North Atlantic. The initiation of the LGM at 27.3 ka is marked by a 4 °C drop in July temperatures, likely responsible for the onset of glacial build-up in the Southern Alpine piedmont. The first extreme continental spell coincides with the British-Irish-sourced IRD event at 26.2 ka and with glacier retreat in the Southern Alps, persisting in the subsequent HS2. Late Glacial glacier collapse and extreme drought occurred during the first half of the HS1, 17.4–16.2 ka. The comparison of the results obtained at Lake Fimon with other terrestrial Eurasian records and with recalibrated marine chronolo

In this paper, we provide a comprehensive overview of the state-of-knowledge of dust flux and variability in time and space in different sectors of East Antarctica during the Holocene. By integrating the literature data with new evidences, we discuss the dust flux and grain-size variability during the current interglacial and its provenance in the innermost part of the East Antarctic plateau as well as in peripheral regions located close to the Transantarctic Mountains. The local importance of aeolian mineral dust aerosol deflated from low-elevation areas of peripheral East Antarctica is also discussed in the light of new data from several coastal, low-elevation sites.

We describe a robust, portable, deployable instrument for multiparametric optical characterization of single airborne particles. It is based on the Single Particle Extinction and Scattering method with additional sensors at 45° and 90° angles. Four independent optical parameters are associated to each particle. Basically, it provides a rigorous measurement of the extinction cross section and the complex amplitude of the forward scattered field. Moreover, thanks to the multiparametric single particle approach, it is possible to roughly classify the particles within a size range from a few hundreds of nanometers to some micrometers. By assigning a reasonable single scattering albedo for each population, our data are enough to fit the phase function with acceptable uncertainties. We report here the results of tests performed with water droplets, generating well controlled data without any free parameters. Data analysis is described in detail. We also report measurements performed on urban aerosol collected in the city of Milan by recovering the optical properties and feeding radiative transfer models. The findings reported here support the importance of an accurate measurement of the phase function, as already established by the Community. Copyright © 2020 American Association for Aerosol Research.

Changes in the composition of dust trapped in ice provide evidence of past atmospheric circulation and earth surface conditions. Investigations of dust provenance in Antarctic ice during glacial and interglacial periods indicate that South America is the primary dust source during both climate regimes. Here, we present results from a new ice core dust archive extracted from the Taylor Glacier in coastal East Antarctica during the deglacial transition from Marine Isotope Stage 6 to 5e. Radiogenic strontium and neodymium isotopes indicate that last interglacial dust is young and volcanic, in contrast to the observed preindustrial and Holocene (Marine Isotope Stage 1) dust composition. The dust composition differences from the last interglacial and current interglacial period at the site require a profound difference in atmospheric transport and environmental conditions. We consider several potential causes for enhanced transport of volcanic material to the site, including increased availability of volcanic material and large-scale atmospheric circulation changes.

We describe an optical approach based on Digital Holography for single-particle characterization of mineral dust and micrometric particles, focusing on the analysis of airborne particles in meltwater from Antarctic ice cores. We record the holograms formed by the superposition of the transilluminating reference beam and the waves scattered by single particles. Taking a cue from recent approaches in the field and holography methods, we process the holograms to recover both optical and morphological properties of single dust grains. As a considerable advantage over traditional light-scattering-based methods, holograms give the extinction cross section of each particle and, by numerically reconstructing the wavefront propagation, an unambiguous image of each particle whereby we derive its cross-sectional shape and size. Measurements have been carried out on samples collected from the recent EAIIST (East Antarctic International Ice Sheet Traverse) project, some of which show evidence of volcanic events. The vast majority of the detected particles show significant deviations from the isometric shape, as confirmed by both image reconstruction and extinction cross section analysis. By our analysis, we observe that experimental data have an extinction cross section up to 3 times lower than that of spherical particles with the same volume. Therefore, these deviations have an appreciable impact on the aerosol contribution to radiative forcing: retrieving particle shape may improve the modeling of the radiative properties of mineral dust and reduce the associated uncertainties.

Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust. However, until now a similar geochemical process was not observed on Earth nor in other planetary settings. We report a multi-analytical indication of jarosite formation within deep ice. Below 1000 m depth, jarosite crystals adhering on residual silica-rich particles have been identified in the Talos Dome ice core (East Antarctica) and interpreted as products of weathering involving aeolian dust and acidic atmospheric aerosols. The progressive increase of ice metamorphism and re-crystallization with depth, favours the relocation and concentration of dust and the formation of acidic brines in isolated environments, allowing chemical reactions and mineral neo-formation to occur. This is the first described englacial diagenetic mechanism occurring in deep Antarctic ice and supports the ice-weathering model for jarosite formation on Mars, highlighting the geologic importance of paleo ice-related processes on this planet. Additional implications concern the preservation of dust-related signals in deep ice cores with respect to paleoclimatic reconstructions and the englacial history of meteorites from Antarctic blue ice fields.

Due to its micrometer-scale resolution and inherently micro-destructive nature, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is particularly suited to exploring the thin and closely spaced layers in the oldest sections of polar ice cores. Recent adaptions to the LA-ICP-MS instrumentation mean we have faster washout times allowing state-of-the-art 2-D imaging of an ice core. This new method has great potential especially when applied to the localization of impurities on the ice sample, something that is crucial, to avoiding misinterpretation of the ultra-fine-resolution signals. Here we present the first results of the application of LA-ICP-MS elemental imaging to the analysis of selected glacial and interglacial samples from the Talos Dome and EPICA Dome C ice cores from central Antarctica. The localization of impurities from both marine and terrestrial sources is discussed, with special emphasis on observing a connection with the network of grain boundaries and differences between different climatic periods. Scale-dependent image analysis shows that the spatial significance of a single line profile along the main core axis increases systematically as the imprint of the grain boundaries weakens. It is demonstrated how instrumental settings can be adapted to suit the purpose of the analysis, i.e., by either employing LA-ICP-MS to study the interplay between impurities and the ice microstructure or to investigate the extremely thin climate proxy signals in deep polar ice.

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We measured saturation isothermal remanent magnetization (SIRM), coercivity of remanence (H-cr), and insoluble dust mass concentration (IDC) of 49 ice samples from Vostok and EPICA Dome-C ice cores (Antarctica) as a measure of magnetic properties of the aerosol dust trapped in the ice. Samples range in age from marine isotopic stage (MIS) 7 to 19 in EPICA Dome-C ice core and from MIS 1 to 11 in Vostok ice core. Data from ice samples were compared with 86 samples from possible source areas (PSA) from East Antarctica, including 11 samples from South America and New Zealand. Previous results from MIS 1 to MIS 6 found that magnetic properties of aerosol dust could be divided in two distinct groups characterized by high-H(cr)and low-SIRM(dust)for glacial samples, and low-H(cr)and high-SIRMdust, for interglacial samples. The new data from older ice samples highlighted several discrepancies from this expectation with significant differences between Vostok and Dome-C sites. Magnetic properties of Antarctic PSA sample show a large variability, however, PSA samples from Victoria Land and few other, have magnetic properties compatible with that of the glacial dust, or more precisely with samples characterized by high dust flux. The new data from Pleistocene ice and from PSA samples confirm South American and Antarctic provenance of the largest atmospheric dust load typical of glacial stages. On the other hand, we did not found any PSA sample with properties compatible with the highly magnetic samples (mostly from interglacial stages), which are characterized by low IDC. These samples from the oldest and deepest part of the cores revealed a more complex picture than previously outlined from the analysis of MIS 1-6, and show unusual magnetic properties which can be tentatively attributed to post-depositional alteration occurring into the ice.

Cryoconite, a sediment found on the surface of glaciers, is known for its ability to accumulate radionuclides. New data on cryoconite from the Morteratsch glacier (Switzerland) are presented to shed light on the mechanisms that control the distribution of radioactivity in cryoconite. Among the radionuclides detected in our samples, we have identified 108mAg, an artificial species which has never been observed in terrestrial environments before. This finding supports that cryoconite has an extraordinary ability to accumulate radioactivity. Our results also show that the radioactivity of cryoconite from a single glacier is far from uniform. Both the absolute amount of radioactivity and the relative contribution of single radionuclides are highly variable in samples from the Morteratsch glacier. To investigate the processes responsible for such variability, we have explored the correlation between radionuclides, organic and inorganic carbon fractions and the morphological features of cryoconite deposits. We have found that the degree of connection between cryoconite and supraglacial hydrology is particularly important, since it strongly influences the accumulation of radionuclides in cryoconite. Cryoconite holes connected with supraglacial channels are rich in cosmogenic 7Be; in contrast, poorly connected deposits are rich in artificial fallout radionuclides and elemental carbon. The very different half-lives of 7Be and artificial radionuclides allowed us to discuss our findings in relation to the age and maturity of cryoconite deposits, highlighting the potential use of radionuclides to investigate hydrological supraglacial processes and material cycling at the surface of glaciers.

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.