Polar ice contains chemical impurities, which can be used as a proxy for the past climate, using state-of-the-art chemical methods. Despite its capability to access critical physicochemical parameters of insoluble particles, such as number concentration, mass and size distribution, and elemental composition, single particle inductively coupled plasma-time of flight mass spectrometry (SP ICP-TOFMS) has yet to be fully utilised to study polar ice. We demonstrate the largely qualitative SP ICP-TOFMS analysis of eight EGRIP ice core samples, which were previously characterised with Raman spectroscopy and laser ablation inductively coupled plasma-mass spectrometry. This resulted in three major developments. First, by analysing samples from different climate periods over the last 50 ka, we extend available ice core SP data to the Younger Dryas and the Last Glacial, and provide an overview of largely unexplored particulate elements in deep polar ice. Second, we develop an approach for handling discrete samples with highly variable particle concentrations, complementing time-intensive continuous analyses despite certain limitations. Third, we suggest adapting an approach for estimating particle sizes based on mineralogical data from previously conducted Raman spectroscopy analyses. This particle size analysis complements established particle sizing and counting techniques by covering the mostly unexplored nanometre range while providing additional chemical information. Overall, we outline the advantages and disadvantages of conducting SP ICP-TOFMS as the final step in a cascade of complementary techniques applied to the same samples. Given the ongoing endeavour to retrieve and analyse precious “Oldest Ice”, utilising SP ICP-TOFMS, even in a more qualitative way, may become critical for accessing vital information and new depths of insight.

The Beyond EPICA–Oldest Ice Core (BE-OIC) project successfully recovered the oldest continuous Antarctic ice core, extending back to at least 1.2 million years. This landmark achievement provides an unprecedented opportunity to address long-standing questions regarding the mechanisms underlying the Mid-Pleistocene Transition (MPT) (Barbante & Beyond EPICA Team, 2025). Among others, this core could be used to study past changes in atmospheric aerosol composition and here, in particular the geochemical composition of mineral dust.However, deep ice is increasingly recognized as a “geochemical reactor”, in which primary mineral impurities undergo post-depositional transformations into secondary phases such as jarosite (Baccolo et al., 2021; Lanci et al., 2025). These alterations pose a major challenge for extracting reliable paleoclimate signals from the analysis of mineral dust trapped into old ice. As such, to avoid misinterpretation of dust-related proxy records, we need to better constrain the nature and extent of deep-ice geochemical processes.Here, we investigate post-depositional geochemical alterations in the EPICA Dome C (EDC) ice core through elemental analysis of ten sections (55 or 110 cm long) spanning the depth of 282 to 3137 m. For the first time, we apply single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS) coupled to the Bern continuous flow analysis (CFA) system to EDC ice core analysis. This approach allows the separate quantification of dissolved and particulate elemental fractions and enables the characterization of the chemical composition of individual particles. Our results reveal extensive dissolution of primary minerals (e.g. hornblende-like phases), accompanied by the precipitation of secondary insoluble and soluble sulfates (e.g. jarosite, alunite), and possibly other Fe-oxide phases. These transformations are likely driven by localized acidic and oxidative microenvironments that develop during the metamorphism of deep ice, depending, to first order, on the growth of ice grains.Our findings provide new insights into post-depositional geochemical processes in deep Antarctic ice and are crucial for ensuring robust paleoclimate reconstructions from dust records in the oldest ice cores, including BE-OIC. Notably, significant geochemical alteration is observed in EDC sections at temperatures of approximately −15 °C and above, indicating that, at the conditions encountered at EDC, these changes emerge at around −15 °C and intensify under warmer conditions. Given that BE-OIC ice of comparable age to EDC is colder while exhibiting similar dust concentration, the BE-OIC ice core may preserve a less geochemically altered, and therefore higher-quality, dust archive for periods already covered by the EDC record (

Introduction: High-altitude glaciers in the Western European Alps have yielded crucial records of anthropogenic air pollution, revealing a sharp rise in pollutant levels over the past two centuries due to industrialisation. In contrast, studies in the Eastern Alps have been scarce, as their lower-elevation glaciers were often considered less suitable for preserving undisturbed records. Nevertheless, recent findings indicate that, under specific conditions, cold ice frozen to bedrock can persist below 4,000 m. This is exemplified by the Wei ss seespitze (WSS) summit ice cap (3,499 m a.s.l.), which, despite ongoing surface mass loss, preserved a 6000-year-old record within just similar to 10 m of ice depth. Methods: Building on earlier research, this study provides an expanded chemical dataset of the upper 8.5 m of the 9.95 m ice core drilled in 2019 (core 2), now including 18 trace elements (Li, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Ag, Cd, Ba, Tl, Pb, Bi, U), carboxylic and dicarboxylic acids, and a deepened discussion on ionic compounds, which refines the already published record. To differentiate between natural contributions and anthropogenic sources, a Positive Matrix Factorisation analysis was applied to the full dataset. This analysis was further supported by Enrichment Factors calculations, which helped to discriminate between crustal and non-crustal sources. Results: Thanks to the novel age-depth scale obtained with Ar-39 dating, in addition to previous C-14 ages, the glacier's age-depth model was further refined, revealing that the glacier surface formed approximately 371 (- 60) (+96) years before 2019, while tying the prominent peak in chemistry found at 640 cm depth to about 891 years before 2019. Further insights on this horizon came from the comparison between the levoglucosan record, measured within the WSS ice core, and the micro-charcoal data available for the nearby Schwarzboden mire. Discussion: This study underscores the exceptional value of the WSS glacier as a long-term archive of pre-industrial pollution. Alarmingly, approximately 4.5 m of ice have been lost as of 2025, accelerating the disappearance of this archive. With industrial-era layers already lost due to ice mass reduction and projections showing 30% of & Ouml;tztal glaciers could vanish by 2030, preserving and studying these records appears increasingly urgent.

Associated with ongoing global warming, prolonged periods of negative mass balance affect even Alpine glaciers in high summit regions, which are also prime candidates for paleoclimate-related ice core studies. This greatly complicates the already challenging task of establishing an age-depth relationship where now both, the age at depth and at the surface is an unknown. Radiometric ice dating methods are an important key to tackle this challenge. This study presents a comprehensive age-depth profile of the summit glacier of Wei ss seespitze (WSS, 3500 m a.s.l.) in the Austrian Alps, utilizing a combination of radiometric dating methods - 39Ar and 14C. Ice cores from drilling campaigns conducted in 2019, 2023, and 2024 were analyzed to overcome challenges posed by extensive ice loss and surface melting that limit traditional dating techniques. All 39Ar samples were measured using atom trap trace analysis (ATTA). Surface mass balance (SMB) data since 2019 were used to align core depths across years, and all samples were referenced to height above bedrock to standardize comparisons.Age modeling using least squares fitting and Monte Carlo sampling was performed for three glaciological models: Nye, Raymond, and a two-parameter (2p) model to test their applicability. The 2p model provided the best fit (chi red2 = 0.4), closely matching the data and providing a continuous age-depth scale. The model yielded a mean accumulation rate of 0.53 m w.e. a-1 (1 sigma range: 0.38-0.63 m w.e. a-1) and a thinning parameter p = 0.92 (1 sigma: 0.81-0.97), the former agreeing with current accumulation estimates.The results show that the surface ice dates back approximately 400 a, emphasizing the extent of recent ice loss. Apart from this, the continuous age-depth relation shows no sign of prolonged periods of mass loss at WSS within the 6000 a glaciation history prior to today.This work underscores the utility of 39Ar dating in alpine glaciology, enabling precise reconstruction of age-depth relationships even under advanced glacial retreat and enhancing our understanding of Holocene climate history in the Eastern Alps.

Abstract. Aerosol-derived impurities in deep Antarctic ice cores provide high-resolution records of past climate and atmospheric variability. However, post-depositional englacial geochemical processes driven by impurity remobilization through ice metamorphism can perturb the originally deposited signals, challenging the interpretation of deep ice records. To address this, we investigate englacial mineral alterations by analyzing the elemental composition of 18 ice-core sections of the EPICA Dome C (EDC) ice core (ranging from 281.6–3137.1 m depth) using single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS) coupled to a continuous flow analysis (CFA) system. This reveals a deep-ice environment dominated by pervasive acid dissolution, leaving behind refractory mineral phases. We document the progressive neoformation of potassium-rich alunite-supergroup minerals (jarosite, alunite, and mixed phases) and the probable formation of Fe-(oxyhydr)oxide coatings. These secondary phases concurrently immobilize trace elements (iodine, arsenic, lead) via surface adsorption and structural substitution. These transformations occur within highly localized microenvironments and are accelerated by increasing in situ temperatures with depth. They are further enabled by the old age of deep ice, which provides hundreds of thousands of years for these reactions to occur. These findings underscore the importance of accounting for the effects of post-depositional geochemical transformation when interpreting impurity records from EDC and other old ice cores. The colder thermal regime of the Beyond EPICA Little Dome C is expected to lead to slower geochemical transformation, potentially providing a higher-fidelity impurity record for the epochs currently covered by EDC.

High-latitude or high-altitude caves often preserve ice deposits that contain valuable signals of past climate conditions, sometimes even reflecting regional and local atmospheric variability. Phases of aggradation or degradation of underground ice can also provide insights into the temporal evolution of Alpine permafrost. Such data are typically obtained from ice cores, which require a well-constrained chronological framework to be meaningful. In recent years, several dating methods have been developed or refined for glacier and ice sheet cores. However, some of these techniques have not yet been applied to cave ice. In this study, the 39Ar dating technique using Argon Trap Trace Analysis is applied for the first time to an underground ice deposit in the southeastern Alps, specifically in the Canin-Kanin massif (Julian Alps). The results are compared with pollen markers extracted from the ice, with U-Th dating of cryogenic cave carbonates found in situ within the same ice block, and with radiocarbon (14C) dating of the water-insoluble organic carbon fraction embedded in the ice. This integrated approach enabled dating the ice deposit to the end of the Little Ice Age, at the onset of the subsequent warming phase.

Particles on the nano- and micro-scale are produced in a wide range of natural and anthropogenic processes and play a significant role in the biogeochemical cycling of major and trace elements in the environment. Single particle inductively coupled plasma - mass spectrometry (SP ICP-MS) is quickly becoming one of the premier techniques for analysis of nano- or micro-entities. However, SP ICP-MS analysis requires dilute aqueous solutions, free from large particles that could cause blockages. For environmentally relevant samples, like soil extracts, this typically calls for sample clean up. Sample preparation strategies like syringe filtration or ultra-centrifugation are regularly applied to handle complex matrices. The aim of this article is to examine the influence of common preparative strategies on the analysis of both naturally formed and synthetic nanoparticles in complex matrices. To achieve this, water extracts of mineral and sediment standards were spiked with Au nanoparticles and a variety of chemical and physical approaches were investigated to identify which strategies provide the best route to accurately quantifying particle numbers, masses and sizes. In a vast majority of cases, at least 90% of the detectable particles were lost for both particle types whenever filtration or centrifugation was applied. The addition of surfactants like Triton X-100 proved to promote relative particle recoveries of up to 30% for spiked Au particles but the extracted Fe-containing particles continued to have losses of up to 99%. Therefore, common sample preparation strategies are directly impeding the possibilities for quantitative particle analysis by SP ICP-MS. Furthermore, commonly used nanoparticles like Au do not necessarily reflect the reality of nano- and microparticles found in the environment. It is apparent that for SP ICP-MS to become a useful, quantitative method for environmental analysis there must be a high degree of care taken in the collection and preparation stages of analysis.

Understanding the spatial variability of impurities in glacier ice on a quantitative level has importance for assessing the preservation of paleoclimatic signals and for the study of macroscopic deformational as well as dielectric ice properties. Two-dimensional imaging via laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) can provide key insight into the localization of impurities in the ice matrix: Employing the relatively recent advances in LA-ICP-MS featuring fast wash-out devices and single laser shot resolution, state-of-the-art LA-ICP-MS imaging has revealed snapshots showing a close association between grain boundaries and some impurities as well as dispersed clusters in dust-rich ice. So far, these findings are mostly qualitative and gaining quantitative insights remains challenging. Accurate calibrations rely on matrix-matched standards which ideally show the same ablation behavior as the sample. Previous studies successfully prepared ice blocks on glass slides as calibration standards at a resolution of a few hundred microns. State-of-the-art LA-ICP-MS imaging fully reveals the imprint of the ice matrix on the impurity distribution at the grain scale, which also introduces the need for new adequate quantification strategies and consequently, the design of new calibration standards. Here, we present different quantification methods, which provide a high level of homogeneity at the scale of a few microns and, which are dedicated to imaging applications of ice core samples. For this purpose, we use small µL volumes and fast freezing techniques. One of the proposed methods has a second application, offering laboratory experiments to investigate the displacement of impurities by grain growth, with important future potential to study ice-impurity interactions. Standards were analyzed to enable an absolute quantification of impurities in selected ice core samples. Calibrated LA-ICP-MS maps indicate similar distributions of impurities in all samples, while impurity levels vary distinctly: Higher concentrations were calibrated in glacial periods and Greenland, and lower levels in interglacial periods and samples from central Antarctica. These results are consistent with known ranges from bulk meltwater analysis. Further comparison with bulk meltwater analysis calls for a more sophisticated representation of the ice chemistry across spatial scales, for which the calibrated LA-ICP-MS maps now also introduce the quantitative domain.

Addressing the intricate challenges of water isotope analysis in polar ice cores, especially in extracting detailed climate records from older and thinner ice layers, the innovative integration of Laser Ablation (LA) with Cavity Ring Down Spectroscopy (CRDS) is introduced. The micro-destructive LA technique, which employs a nanosecond excimer pulsed laser operating at 193 nm for ice surface irradiation, demonstrates potential in achieving continuous, high-resolution sampling and gas phase sample generation, complementing the CRDS analyzer's precision in measuring water isotopes in gaseous state. Recent advancements include the successful adaptation of an existing LA system, previously coupled with an Inductively Coupled Plasma - Mass Spectrometer (ICP-MS) for ice core impurity analysis, to establish a connection with the CRDS analyzer. This was accomplished by making adjustments to the coupling procedure and laser parameters, to ensure efficient gas sample generation and robust delivery for water isotope analysis. A method for creating ice standard samples by transforming liquid water standards into ice yielded ice isotope standards, crucial for setting up initial measurement protocols. Their implementation on both standard ice samples and sections of ice cores revealed valuable insights into areas for improvement. This represents a significant step towards establishing a reliable method for high-quality water isotope analysis in ice cores, aiming to significantly enrich our understanding of long-term climate trends.

Recent advances in high-repetition-rate lasers and fast aerosol transfer facilitate laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping rates of up to megapixels per hour, however, practical limits in time and resources still hamper mapping the chemistry of square centimetre or larger areas of target samples at high resolutions. This is especially relevant for the analysis of deep sections of polar ice cores, motivating exploration of approaches to improve the efficiency of LA-ICP-MS data collection for large-area mapping. Assisted by computer vision, and demonstrated on glass and ice samples, we show how an informed experimental design coupled with computational post processing can contribute to large reductions in measurement times and lead to associated increases in measurement areas. Using various inpainting techniques, we demonstrate how the collection of data can be reduced by up to two thirds while still capturing spatial variability. Although motivated by ice core analysis, these approaches are generalisable to other target matrices and represent a new approach to large-area LA-ICP-MS mapping.

High-altitude glaciers in the western European Alps have preserved long-term records of anthropogenic air pollution, as shown by numerous ice core studies over the past three decades. These records reveal a significant increase in pollutants over the last two centuries, closely linked to industrialization, with pollutants transported from nearby regions. In contrast, long-term studies in the eastern Alps remain limited, as these glaciers were considered unsuitable for undisturbed ice core preservation due to their lower elevations and temperate basal conditions. However, recent findings suggest that, under specific circumstances, cold ice frozen to bedrock can exist below 4000 m, as demonstrated by the Weißseespitze (WSS) summit ice cap in the Eastern Alps (3499 m a.s.l.), which preserves a 6000-year-old record within ~10 m of depth, despite ongoing surface mass loss.Building on earlier work, this study provides further insights into the WSS glacier through expanded chemical analyses of an 8.5 m deep ice core drilled in 2019, complementing previously reported data on major ions and levoglucosan. The extended dataset includes detailed profiles of 22 trace elements (Ag, As, Ba, Be, Bi, Cd, Co, Cr, Cu, Ga, In, Li, Mn, Ni, Pb, Rb, Se, Sr, Tl, U, V, Zn), carboxylic and dicarboxylic acids, obtained from discrete samples collected alongside the 2022 melting campaign performed at Ca’ Foscari University.A Positive Matrix Factorization (PMF) analysis of the recorded impurities revealed significant anthropogenic contributions to the trace element profiles. This was supported by a Lagrangian particle dispersion model, showing that ~50% of the air masses over the WSS glacier originated in Central Europe, with a notable contribution from the Po Valley, emphasizing its historical role in pollution transport.To refine the glacier's age-depth relationship and contextualize these findings, age constraints were obtained from micro-14C dating and 39Ar dating using atom trap trace analysis (ATTA) from a parallel ice core and additional shallow cores, integrated with the chemical dataset. This analysis determined that the glacier surface formed approximately 356 +19 -23 years prior to 2019. Additionally, the dating established a precise timeline for a significant levoglucosan and chemical peak at a depth of 6.4 meters, placing it roughly 779 +53 -63 years before 2019. The radiometric age data were combined with an age model using the Raymond model, suitable for ice cap conditions like WSS.Building on these insights, the regional significance of the prominent horizon at 6.4 m depth in the 2019 Weißseespitze ice core was explored by comparing the levoglucosan record with micro-charcoal data from the Schwarzboden mire in the Maneid valley, a few kilometers southeast of the glacier. This comparison revealed a striking correspondence, offering new insights into the region’s environmental history.This study highlights the WSS glacier’s exceptional value as a long-term archive of pre-industrial pollution. However, with the industrial period already erased by ice mass loss, this archive is critically endangered. Projections suggest that 30% of the Ötztal glaciers could vanish by 2030, emphasizing the untapped potential of Eastern Alpine glaciers in reconstructing past environmental changes before they disappear.

Ice cores can supply high-resolution insights into abrupt changes within the climate system. The RECAP ice core from the Renland ice cap, East Greenland, contains a substantial variety in dust particle size throughout its record, reaching back to the Eemian. Changes in dust particle sizes have been shown to reflect smaller ice cap extent during interglacial periods. Thus, local dust sources are only periodically available and can be characterised by large dust particles. For abrupt changes during the last glacial period, it is necessary to disentangle the potential imprint of dust sources and the role of snow accumulation. To better understand dust chemistry and size changes at high resolution, we apply several analytical methods in an ongoing investigation: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) 2D imaging, coulter counter (CC), time-of-flight single particle analysis (SP ICP-TOFMS), and Low- Background Instrumental Neutron Activation Analysis (LB-INAA). We show that high-resolution (10-40 µm) 2D chemical images, focusing on Na, Al, Mg, and Fe, reveal the clustering of particles in the microstructure and a species-dependent preferred localisation. Subsequent measurements, taken where possible on the same samples provide new insoluble particle size and concentration data (CC) and further in-depth elemental characterisation of the dust particles (LB-INAA). Furthermore, first results from SP analyses display their potential for ice core research regarding largely unexplored areas, such as the characterisation of rare earth elements of dust deposited in Greenland. The expertise and insight on high-resolution dust chemistry and size gained during this multi-method approach on ice with partly highly thinned annual layers will eventually be crucial for interpreting the dust signal stored in future Antarctic ice cores reaching back up to 1.5 Myr.

Aerosol-related impurities play an important part in the set of paleoclimate proxies obtained from polar ice cores. However, in order to avoid misinterpretation, post-depositional changes need to be carefully assessed, especially in deep ice. Na, S and Cl are among the relatively abundant impurity species in polar ice (albeit still at the low ppb level in bulk samples), with important applications to paleoclimate reconstructions and dating, e.g. via identification of volcanic eruptions. Especially S has been studied intensely with respect to peak broadening with depth/age related to diffusion, but the precise physical mechanisms remain unclear. Mapping the two-dimensional impurity distribution in ice with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has shown great potential for studying ice-impurity interactions, but the analytically more challenging elements S and Cl have not been targeted thus far. We show here that signals of S and Cl can be detected in Greenland and Antarctic ice by LA-ICP-MS mapping. In ice without evidence of volcanic activity, and unenhanced impurity concentrations, we obtain multi-elemental maps for Na, Cl and S at high resolution up to 10 µm and also include some exemplarily high resolution maps with a spot size down to 1 µm. We use Na as a previously investigated reference element and find a high level of localization of Na, S and Cl at grain boundaries but also some dispersed occurrence within grain interiors in dust-rich ice. The new maps support a view on diffusive transport not only through ice veins but also along grain boundaries. In the EPICA Dome C ice core samples we do not find any clear differences in impurity localization between samples from the Holocene and last glacial period. These results extend early studies targeting the localization of impurities, in particular through measuring S and Cl, and highlight the benefit of integrating such direct measurements with modelling efforts to determine the physical processes behind impurity diffusion.

The single particle inductively coupled plasma time-of-flight mass spectrometer (sp-ICP-TOFMS, model: icpTOF R from TOFWERK, Switzerland) coupled to the Bern continuous flow analysis (CFA) has demonstrated its ability to resolve signals of individual insoluble particles in the meltwater. This offers valuable insights into the characteristics of mineral dust obtained from the elemental composition of the mineral dust as - in contrast to bulk analyses - it allows deciphering of the complete elemental range of particle composition, which can be a mixture of different minerals (Erhardt et al. 2019). To apply this new technique for the first time to sections of an Antarctic ice core covering several glacial and interglacial stages, we conducted aerosol chemical CFA measurements on a selection of 18 Antarctic EPICA Dome C (EDC) 55 cm ice core sections, from both glacial and interglacial periods over the last 800 kyr using CFA-sp-ICP-TOFMS.We present the new preliminary results of our CFA campaign with a nominal 55 cm bag mean resolution (or 110 cm where two consecutive bags were measured). The depth resolution corresponds to a time period in the range of 40 to 602 years of precipitation history in the Holocene, the last glacial period, and various marine isotope stages (MIS 9, 11, 15, 16, 17, and 18). Our goal is to extract detailed information about changes in climate and environmental conditions from individual elemental mineral dust particles. We compare the element-bearing particle number concentration (PNC) measured with sp-ICP-TOFMS for both major and minor crustal elements to the dust PNC optically measured with a laser absorption particle sensor (Abakus from Klotz, Germany), irrespective of its elemental composition, providing a complementary perspective. Furthermore, we examine the variability of dust composition using the elemental mass ratio of individual mineral dust particles during different warm and cold periods.

Measuring aerosol-related impurities in ice cores gives insight into Earth's past climate conditions. In order to resolve highly thinned layers and to investigate post-depositional processes, such measurements require high-resolution analysis, especially in deep ice. Micron-resolution impurity data can be collected using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), but this requires careful assessment to avoid misinterpretation. Two-dimensional (2D) imaging with LA-ICP-MS has provided significant new insight, often showing an association between soluble impurities and the ice crystal matrix, but interpreting one-dimensional (1D) signals collected with LA-ICP-MS remains challenging partially due to this impurity–boundary association manifesting strongly in measured signals. In this work, a computational framework has been developed, integrating insights from 2D imaging to aid the interpretation of 1D signals. The framework utilises a simulated model of a macroscopic ice volume with a representative microstructure and soluble impurity localisation that statistically represents distributions seen in 2D maps, allowing quantitative assessment of the imprint of the ice matrix on 1D signals collected from the volume. Input data were collected from four ice core samples from Greenland and Antarctica. For the samples measured, quantifying the variability in 1D signals due to the impurity–matrix imprint shows that modelled continuous bulk signal intensity at the centimetre scale varies below 2 % away from an idealised measurement that captures all variability. In contrast, modelled single-profile micron-resolution LA-ICP-MS signals can vary by an average of more than 100 %. Combining individual LA-ICP-MS signals into smoothed and spatially averaged signals can reduce this variation to between 1.5 and 5.9 %. This approach guides collecting layer-representative signals from LA-ICP-MS line profiles and may help to bridge the scale gap between LA-ICP-MS data and data collected from meltwater analysis.

Impurity records in polar ice cores have provided invaluable insights into atmospheric aerosol concentrations of the past environment. The investigation of the oldest, deepest and highly thinned ice core layers is one of the most pressing tasks in today’s state-of-the-art ice core research. This calls for impurity analysis at high spatial resolution, which has to take into account post-depositional processes through the interaction of impurities with the ice matrix. To this end, mapping the impurity distribution in ice with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) has great potential. Here we explore to what extent the use of Ar as a carrier gas has merits in ice core impurity mapping with LA-ICP-MS. This is motivated by the fact that a) the use of Ar is more economical over He, especially when used in conjunction with large volume sample cells, and b) an increase in sensitivity has previously been reported when adding ”wet” Ar to He as a carrier gas. We show that, albeit not fully matching the single-pulse-performance of He, it is possible to achieve mapping at up to 500 Hz with Ar in a system that is originally designed for He. In contrast to what we find on NIST glass standards and a sample of decorative murrina glass, maps obtained on ice core samples show higher intensities in Ar than in He. In an extreme case example, we show how Ar may permit to obtain signals in a deep interglacial ice sample from Antarctica with very low impurity concentrations, which was not possible when using He with the same LA-ICP-MS system.

Ice that will be extracted from close to the bedrock of the Antarctic ice sheet during the Beyond EPICA Oldest Ice (BE-OI) project is expected to have more than 14,000 years of climatic information contained in a single vertical meter of ice. High-resolution analysis is required to extract meaningful climate signals from the impurities contained in this ice. This analysis should be comparable to the currently established continuous flow analysis (CFA) approach, which acquires a 1-dimensional impurity signal at approximately centimetre resolution. To date, it has been shown that smoothed high-resolution profiles taken using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are comparable to CFA signals. However, the physical origin of this link needs to be better understood, especially in view of the imprint of the impurities on the ice crystal matrix recently revealed by 2D imaging on the micron scale. Here we present a framework to generate and explore 3-dimensional models mapping the location of soluble impurities within ice samples. This framework helps link experimentally acquired smoothed LA-ICP-MS profiles, 2-dimensional LA-ICP-MS maps of impurities, and CFA data. The conceptual step into 3-dimensions allows exploration of the distortions of the climate signal due to interactions of impurities with the ice matrix. In shallow ice with relatively small grains and well resolved stratigraphy, this distortion is likely not significant enough to compromise analysis that takes large sample volumes with large mixing, such as seen during CFA. In order to extract signals in deep ice with large crystal sizes and dense layering, where this distortion will be most relevant, we find that carefully designed LA-ICP-MS experiments coupled with post-processing upscaling techniques are required. For a test against experimental data, this work is now being applied to a comparative study involving Antarctic ice measured with both CFA and LA-ICP-MS systems to prove its application to shallower, better-understood ice intervals. Ultimately, the goal is to develop a combination of cm-scale CFA, micron-scale LA-ICP-MS imaging and 3D modelling that will provide key insight on the impurity-related climate signals in deep ice at the BEOI core and elsewhere.