Geunwoo Lee

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.

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.

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.

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.

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.

Polar ice cores are archives of past climate conditions and atmospheric composition. Atmospheric aerosols deposited on the ice sheets and subsequently preserved in the ice provide detailed records of past atmospheric conditions. Analyses of these impurities therefore offer valuable insights into environmental changes in the past.Here we present high-resolution impurity records from the East Greenland Ice Core Project (EGRIP) ice core measured with the University of Bern continuous flow analysis (CFA) set-up. Continuous melting and the analysis of only the inner part of the ice stick allows for high resolution while minimizing contamination. The analyzed components include water-insoluble dust particles as well as the dissolved impurities calcium, ammonium, and nitrate. For the dust record, we focus on the previously not studied changes in the main mode of the dust number concentration (

Particulate mineral dust is a critical part of the Earth’s climate system, modulating radiative balance and providing a crucial source of micronutrients to surface oceans. In ice cores, mineral dust also serves as a key proxy for past atmospheric dynamics - controlling dust mobilization and transport - as well as hydroclimate variability, which affects the atmospheric residence time of dust in addition to emission strength in the source regions. Previous studies, including those from the 800,000-year EPICA Dome C ice core, have demonstrated a close coupling between dust particle number concentrations in ice cores and glacial-interglacial climate variability, with consistently higher dust concentrations during cold glacial periods. The new Beyond EPICA-Oldest Ice Core (BE-OIC: 75º 18’ S, 122º 27’ W) extends the existing ice core particulate dust record back through the Mid-Pleistocene Transition (MPT), providing new constraints on this enigmatic period in Earth’s climate history.We present the first continuous record of particulate mineral dust particle size and particle number distributions from the new BE-OIC, spanning from 700,000 years BP through the Mid-Pleistocene Transition. Physical characteristics of individual dust grains were measured online by the University of Bern during the Continuous Flow Analysis measurement campaign at the British Antarctic Survey using dual Classizer One Single Particle Extinction and Scattering instruments (EOS) and an Abakus laser particle sensor (Klotz GmbH), enabling characterization of particle concentration, dust size but also its refractive index over a wide range of diameters (0.2–10 µm). The latter is crucial as it allows us for the first time to resolve the submicrometer mode in the number size distribution.Consistent with earlier work on the EDC ice core, the new BE-OIC record shows elevated dust concentrations during glacial periods both before, during and post MPT. However, the amplitude of glacial-interglacial variability is reduced relative to the past 800,000 years. In addition, modal particle diameters in the number size distribution are smaller during glacials compared to interglacials, indicating enhanced contributions from long-distance dust transport during the colder climate states. We investigate the processes that lead to dust size and number changes, including how reduced glacial intensity pre-MPT may have impacted dust source regions and the atmospheric lifetimes of dust particles. Together, these observations indicate changes in dust source-to-sink dynamics that have implications for biogeochemical cycles in the Southern Ocean and atmospheric dynamics during the MPT.

Mineral dust concentration and grain size preserved in polar ice cores serve as critical paleoclimate proxies spanning the Holocene and Pleistocene epochs. These parameters yield valuable information about past environmental conditions in dust source regions, atmospheric dust loading and transport dynamics, exhibiting pronounced variability across glacial–interglacial cycles. The Antarctic dust deposition record derived from the ∼800.000 years old EPICA Dome C (EDC) ice core has now been extended further back into the Early Pleistocene through analysis of the Beyond EPICA-Oldest Ice Core (BEOIC). Here we present the preliminary Coulter Counter-derived dust concentration (0.6-18 μm range) and volume-size data from BEOIC for the period predating the EDC record, and compare them with available marine dust records. Dust concentration and grain size variability in the oldest ice enable the identification of glacial and interglacial periods, with characteristic size distributions showing relatively coarser particles during interglacials and finer particles during glacials.The use of aeolian dust as a paleoclimatic proxy in ice cores assumes that englacial processes preserve the original physical and chemical signals. However, this paradigm has been partially challenged by evidence of in situ alteration processes that induce physical and geochemical (including mineralogical) modifications within the ice. The extent and nature of these processes in the BEOIC are currently under investigation. Preliminary observations are presented and compared with findings from other Antarctic ice cores (TALDICE, RICE) to evaluate the reliability of paleoclimatic signal preservation in the oldest ice sections.

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 (

Ice cores serve as unique paleo-archives allowing access to long-term records of trace elements, which are important for our understanding of global biogeochemical cycles and air pollution. However, analysis of trace elements in ice cores is a challenge, because of very low concentration levels and their presence in dissolved and particulate form. The commonly used and well-established technique for analysis of trace elements in ice cores is inductively coupled plasma sector field mass spectrometry (ICP-SF-MS). Recently, inductively coupled plasma time of flight mass spectrometry (ICP-TOF-MS) was introduced as a new, promising technique. Due to its fast acquisition time for the near-full mass spectral range, it allows for the detection of short transient signals, offering the opportunity to determine the elemental composition of single particles. In this study, the performance of this new technique for analyzing total trace element concentrations was tested and compared to the one established in the field of ice core research. The focus was on sensitivity, precision, and optimization of sample preparation in sections from two ice cores (Colle Gnifetti, Cerro Negro), characterized by different impurity levels. The performance of the ICP-TOF-MS was excellent for the investigated trace elements within the nominal mass range from 23 to 238, except for ⁴⁵Sc because of insufficiently resolved mass interferences. This is very promising for many applications in ice core research, especially in view of the great benefit to analyze single particles simultaneously in the same sample.