Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH₄) to short-lived trace gases like ethane (C₂H₆) and propane (C₃H₈). Interpreting these data in terms of atmospheric changes requires that the analyzed species accurately reflect the past atmospheric composition.

Recent comparisons of Greenland CH₄ records obtained using different extraction techniques revealed discrepancies in the CH₄ concentration for the last glacial. Elevated methane levels (excess methane or CH_4(exs)) were detected in dust rich ice core sections measured by discrete melt extraction techniques pointing to an artefact sensitive to the measurement technique. To shed light on the underlying mechanism, we analyzed Greenland ice core samples for methane and other short-chain alkanes (ethane and propane) covering the time interval from 12 to 42 kyr using a classic wet extraction technique. The artefact production happens during the melting and extraction step (in extractu) and reaches 14 to 91 ppb CH_4(exs) in dusty ice samples. For the first time in ice core analyses, we document a co-production of excess methane, ethane, and propane (excess alkanes) with the observed concentrations for ethane and propane exceeding, at least by a factor of 10, their past atmospheric concentration. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14:2:1, indicating a common production. We also discovered that the amount of excess alkanes scales generally with the amount of mineral dust (or Ca²⁺ as a proxy for mineral dust) within the ice samples. Moreover, applying the Keeling-plot approach we are able to isotopically characterize CH_4(exs) revealing a relatively heavy carbon isotopic signature of (-46.4 ± 2.4) ‰ and a light deuterium isotopic signature of (-326 ± 57) ‰ of the excess methane in the samples analyzed.

The co-production ratios of excess alkanes and the isotopic composition of excess methane allows us to confine potential formation processes. We discovered that this specific alkane pattern is not in line with an anaerobic methanogenic origin but indicative for abiotic decomposition of organic matter as also found in sediments, soils, and plant leaves. From the present-day state of research little is known about this process and there is urgent need to improve our understanding for future ice core measurements. Moreover, the already existing discrete records of atmospheric CH₄ in Greenland ice need to be corrected for excess CH₄ contribution (CH_4(exs), δ¹³C-CH_4(exs), δD-CH_4(exs)) in dust-rich intervals.

While the size of the excess methane production has little effect on reconstructed radiative forcing changes of CH₄ in the past, it is in the same range as the Inter-Polar Difference (IPD) for CH₄. Knowing the empirical relation of excess CH_4(exs)/ Ca²⁺ and CH_4(exs)/ C₂H₆ allows us to derive a first-order correction of existing CH₄ data sets to revise previous interpretations of the relative contribution of high latitude northern hemispheric CH₄ sources based on the IPD.

How to cite: Mühl, M., Schmitt, J., Seth, B., Lee, J. E., Edwards, J. S., Brook, E. J., Blunier, T., and Fischer, H.: Excess methane, ethane, and propane production in Greenland ice core samples and a first characterization of the δ13C-CH4 and δD-CH4 signature, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-157, https://doi.org/10.5194/egusphere-egu23-157, 2023.

The assessment of global warming and its far-reaching influences on our planet necessitates reliable and accurate climate models. For this purpose, past atmospheric conditions like aerosol composition must be studied to understand their influence on the Earth’s climate. Ice cores are valuable climate archives that preserve organic compounds from atmospheric aerosols, which can be utilized as marker species for their respective emission sources.

Secondary organic aerosols (SOAs) are formed in the atmosphere by the oxidation of volatile organic compounds (VOCs), which can be either of anthropogenic or biogenic origin. The most common precursors of SOAs are monoterpenes, which are naturally emitted by vegetation in large amounts. Furthermore, organic compounds formed during biomass burning events contribute to the aerosol budget and allow the reconstruction of paleo-fire activity. Of great interest as a marker species is the anhydrosugar levoglucosan, which is formed during the combustion of cellulose. In addition to its combustion products, intact polymeric lignin, digested via alkaline oxidative degradation, can provide information about the type of vegetation which it originated from. A large variety of these markers were analyzed in an ice core extracted from the Belukha glacier located in the Altai region of Southern Siberia covering a time span of three centuries. A sample preparation method including multiple solid phase extractions and UHPLC-HRMS analysis was employed.

Chiral compounds have the same molecular formula and atom connectivity but act like mirror images of each other. In most environmental studies, no distinction is made between these so-called enantiomers. However, chirality can affect chemical and physical properties and thus influence particle formation reactions in the atmosphere. The enantiomeric ratio of a chiral compound can also further elucidate possible emission sources. Here we present the first chiral analysis of monoterpene oxidation products in ice cores and thus on a long-term scale. For this purpose, a multiple heartcut two-dimensional liquid chromatography method (mLC-LC) was developed that allows the simultaneous determination of the enantiomeric ratios of the monoterpene oxidation products cis-pinic acid and cis-pinonic acid in complex ice core samples. This novel method was successfully applied to Belukha ice core samples.

How to cite: Schäfer, J., Burgay, F., Singer, T., Schwikowski, M., and Hoffmann, T.: Analysis of organic aerosol markers and chiral compounds in an ice core from the Siberian Altai using UHPLC-HRMS, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9346, https://doi.org/10.5194/egusphere-egu23-9346, 2023.

Atmospheric heavy metal pollution caused by metal smelting, mining, waste incineration and fossil fuel combustion presents a significant issue for human health and the environment. Anthropogenic emissions from the territory of the former Soviet Union (FSU) considerably influenced atmospheric concentrations of heavy metals. However, due to scarce monitoring data and fragmentary reporting, emissions quantities from this region are not well-known and it is even unclear if emissions decreased or increased after collapse of the Soviet Union. This is underlined by the fact that existing ice-core records and emission estimates based on national inventories for the FSU reveal an opposing trend for the most recent ~30 years. 

Here we present new records of post-Soviet Union anthropogenic heavy metal  emissions (Bi, Cd, Cu, Pb, Sb, Zn) derived from three ice cores; from the Mongolian Altai (Tsambagarav ice core, period 1710-2009 AD) and the Siberian Altai (two Belukha ice cores, period 1680-2018 AD), covering a large regional footprint of emissions. The major source region of air pollution arriving at the Altai is primarily the territory of the FSU except for the eastern-most Siberian parts. Heavy metal concentrations at ultra-trace levels in the studied ice cores were analysed using inductively coupled plasma sector-field mass spectrometry (ICP-SF-MS). These records were complemented with new heavy metal emission estimates based on the available inventory data (1975-2015 AD) to derive a robust reconstruction of recent FSU heavy metal emissions. Consistent with the emission estimates, ice-core concentrations of Cd, Cu, Pb, Sb, Zn during the 2010s correspond to 20-40% of the maximum values in the 1970s and are comparable to their 1940s-1950s levels. A similar magnitude was also estimated for the decrease in Bi between 1975 and 2015, however, ice-core concentrations do not show a substantial downward trend.

How to cite: Eichler, A., Nalivaika, P., Jenk, T., Singer, T., Kakareka, S., Kukharchyk, T., Eyrikh, S., Papina, T., Plach, A., and Schwikowski, M.: Recent heavy metal pollution from the territory of the former Soviet Union (FSU) – ice core records and emission estimates, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12385, https://doi.org/10.5194/egusphere-egu23-12385, 2023.

The National Science Foundation Ice Core Facility (NSF-ICF, fka NICL) is in the process of building a new facility including freezer and scientist support space. The facility is being designed to minimize environmental impacts while maximizing ice core curation and science support. In preparation for the new facility, we are updating research equipment and integrating ice core data collection and processing by assigning International Generic Sample Numbers (IGSN) to advance the “FAIR”ness and establish clear provenance of samples, fostering the next generation of linked research data products. The NSF-ICF team, in collaboration with the US ice  core science community, has established a metadata schema for the assignment of IGSNs to ice cores and samples. In addition, in close coordination with the US ice core community, we are adding equipment modules that expand traditional sets of physical property, visual stratigraphy, and electrical conductance ice core measurements. One such module is an ice core hyperspectral imaging (HSI) system. Adapted for the cold laboratory settings, the SPECIM SisuSCS HSI system can collect up to 224 bands using a continuous line-scanning mode in the visible and near-infrared (VNIR) 400-1000 nm spectral region. A modular system design allows expansion of spectral properties in the future. The second module is an updated multitrack electrical conductance system. These new data will guide real time optimization of sampling for planned analyses during ice core processing, especially for ice with deformed or highly compressed layering. The aim is to facilitate the collection of robust, long-term, and FAIR data archives for every future ice core section processed at NSF-ICF. The NSF-ICF is fully funded by the National Science Foundation and operated by the U.S. Geological Survey.

How to cite: Powers, L., Kurbatov, A., Kershaw, C., Hargreaves, G., Labombard, C., and Fudge, T. J.: The next generation U.S. National Science Foundation Ice Core Facility: supporting state-of-the-art science., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1684, https://doi.org/10.5194/egusphere-egu23-1684, 2023.

Diffusive smoothing of signals on the water stable isotopes in ice sheets limits the climatic information retrievable from these ice-core proxies. Previous theories explained how, in polycrystalline ice below the firn, fast diffusion in the network of intergranular water veins short-circuits the slow diffusion in crystal grains to cause “excess diffusion”, enhancing the signal smoothing rate above that implied by self-diffusion in ice monocrystals. However, the controls of excess diffusion remain poorly understood. I show that vein-water flow amplifies excess diffusion, by altering the three-dimensional field of isotope concentrations and isotope transfer between the veins and crystals. The rate of signal smoothing depends not only on temperature, vein and grain sizes, and signal wavelength, but also on vein-water flow velocity, which can increase the rate by 1 to 2 orders of magnitude. This modulation can significantly impact signal smoothing at ice-core sites in Greenland and Antarctica, as demonstrated by simulations for the GRIP and EPICA Dome C sites, which show sensitive modulation of their diffusion-length profiles when vein-water flow velocities reach ~ 10¹–10² m yr^–1. Thus vein-flow mediated excess diffusion may help explain the mismatch between modelled and spectrally-derived diffusion lengths in other ice cores. I also show that excess diffusion biases the spectral estimation of diffusion lengths from isotopic signals and the reconstruction of surface temperature from diffusion-length profiles. These findings caution against using the single-crystal isotopic diffusivity to represent the bulk-ice diffusivity. The need to predict excess diffusion in ice cores calls for extensive study of isotope records for its occurrence and better understanding of vein-scale hydrology in ice sheets.

How to cite: Ng, F.: Isotope diffusion in ice enhanced by vein-water flow, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10179, https://doi.org/10.5194/egusphere-egu23-10179, 2023.

Water isotopes in ice cores offer a window into the climate of the past. Often the measurement of these water isotopes is done discretely, with the ice cores cut into many regularly spaced samples. Determining the optimal sampling rate for these measurements is a question of balancing high temporal resolution with processing time and effort. Furthermore, the effect of isotopic diffusion smooths the record, attenuating high frequency variability far below the measurement noise level. This results in some climate information becoming unobtainable and limits the usefulness of very high resolution data. Deconvolving (un-diffusing) the time-series can further enhance the signal but strongly depends on the precision of the isotope data that is mainly determined by the measurement error.

Here, we discuss the optimal measurement specifications in terms of sampling resolution and precision for different uses of the water isotope data, such as the estimation of the diffusion length, the direct interpretation of the time-series and the interpretation of the time-series after it has been deconvolved. We do this theoretically, based on how we model diffusion, and empirically through simulations of surrogate ice core records. Our findings can provide guidance on how to process new deep ice cores such as the Oldest Ice Core record.

How to cite: Shaw, F., Dolman, A., Kunz, T., Gkinis, V., and Laepple, T.: Optimal sampling resolution for water isotope records in ice cores, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8369, https://doi.org/10.5194/egusphere-egu23-8369, 2023.

We report interlaboratory comparisons of a methodology to measure and calculate concentrations of impurities in ice core samples using the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) system developed at the W. M. Keck Laser Ice Facility at the Climate Change Institute, University of Maine (UMaine). Here, we will summarize results of measured artificial samples with known levels of  Ca, Al, Fe, Mg, Na, Cu, Pb. We adapted a method for LA-ICP-MS analysis of the frozen standard that was developed in the laboratory at Ca’ Foscari University of Venice, and we tested its applicability to the UMaine system. This work will help to measure and interpret very old and highly compressed ice core records from the Allan Hills Blue Ice Area, Antarctica, sampled with different analytical tools.  

How to cite: Gadrani, L., Kurbatov, A. V., Korotkikh, E., Bohleber, P., Mayewski, P. A., and Handley, M.: Interlaboratory Calibration for Laser Ablation of Ice Cores, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14910, https://doi.org/10.5194/egusphere-egu23-14910, 2023.

Research over the last five years dedicated to identifying and quantifying the processes responsible for driving the climate signal in the isotopic composition of the snow have documented the role of the humidity exchange between the snow and atmosphere in changing the initial precipitation isotopic composition. Laboratory and field experiments combined with direct vapor isotope flux measurements have shown that not only does the depositional flux changes the surface snow isotopic composition, but sublimation from the snow surface induces isotopic fractionation leading to changes in the snow isotopic composition. Thus, it was shown that for the EastGRIP ice core location, including fractionation during sublimation, atmosphere-snow exchange processes explain between 35 and 50 % of the day-to-day variations in the snow surface signal when no precipitation occurs.

Until recently, it was unknown on which time scales these surface exchange processes are important for the isotope signal.

Here we combine direct accumulation and eddy-covariance humidity flux measurements with high resolution regional climate model simulations. Focusing on the EastGRIP ice core site, we find that during the summer season up to 40% of the accumulation is sublimated and about 10% is re-deposited. Such relative high fluxes compared to the amount of precipitated snow would naturally lead to an influence of the seasonal isotopic composition of the snow.

By combining outputs from an isotope-enabled general circulation model (ECHAMwiso) and a regional polar climate model (MAR) with the SNOWISO exchange and snowpack model, we find that the influence on the snowpack isotopic composition is not only isolated to the summer isotope signal but influences the full seasonal cycle. In fact, we find that that the atmosphere-snow exchange influence on the annual mean isotopic composition results in a significant bias in the source region condition deduced from the isotopic composition of the ice core.

How to cite: Steen-Larsen, H. C., Dietrich, L., Wahl, S., Town, M., Hughes, A., Hoerhold, M., Zuhr, A., Behrens, M., Fettweis, X., and Werner, M.: On the importance of atmosphere-snow humidity exchange for the climate signal stored in the snow isotopic composition, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14700, https://doi.org/10.5194/egusphere-egu23-14700, 2023.

The radioisotope Plutonium-239 (²³⁹Pu) was artificially produced to the environment by atmospheric nuclear weapons tests during 1940-1980 CE. Although ²³⁹Pu is the most abundant one among isotopes of Plutonium, it exists in Antarctic ice cores at very low level of sub-fg g^-1. Accordingly, the historical records of ²³⁹Pu fallout in Antarctica have not been well reconstructed. In this study, we determined ²³⁹Pu concentrations in three coastal ice cores in Northern Victoria Land, East Antarctica. Discrete samples with sub-annual resolution for the period 1940-1980 CE were analyzed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS) without purification or preconcentration. The fallout records of the three sites showed consistent fluctuations and also agreed with the records recovered from inland dome sites (Hwang et al., 2019), which allowed for constructing an Antarctic composite record. The composite ²³⁹Pu record was characterized by two major peaks in 1954 and 1964 CE and a minor peak in 1970s, which could be ascribed to the major atmospheric nuclear test events. Those synchronous ²³⁹Pu peaks are expected to serve as useful age markers in other regions in Antarctica, which can improve depth-age relationships of ice core records and enable more precise interregional comparisons. In addition, it will contribute to a more precise comparison of ice core records with reanalysis data back to the 1950s (e.g., ERA5).

How to cite: Shin, J., Lee, S., Hwang, H., and Han, Y.: 239Pu concentrations reconstructed using three Antarctic ice cores during 1940-1980 CE, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2498, https://doi.org/10.5194/egusphere-egu23-2498, 2023.

Oxygen isotopes of snow, firn, and ice cores provide valuable information on past climate variations. Yet, multiple processes, such as stratigraphic noise and the advection of spatial isotope variations linked to topographic anomalies create non-climatic variations (‘noise’) in the ice-core record and limit the quality of high-resolution climate reconstructions. All of these processes are site specific and vary depending on the environmental conditions at and around the ice-core location.  In the last years, based on field studies, numerical experiments and theoretical considerations, we improved our quantitative understanding of these noise generating processes and their dependency on the depositional conditions. Building on this work, we here ask the question how the potential quality of ice-core based climate reconstructions depends on the drilling site location.  Making use of digital elevation models,  ice flow-velocity maps and statistical relationships between the surface topography, accumulation anomalies,  isotopic anomalies and stratigraphic noise, we predict the site and time-scale dependent noise contribution to ice-core records of the last millennium. The created maps provide a step towards choosing optimal ice coring and  sampling locations for high-resolution climate reconstructions from Antarctic ice-cores and provide testable predictions for the quality of future ice-core records.

How to cite: Laepple, T., Dallmayr, R., Hörhold, M., Hirsch, N., Jansen, D., Behrens, M., Münch, T., and Freitag, J.: Optimal coring locations for high resolution climate reconstructions from the East Antarctic Plateau, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14208, https://doi.org/10.5194/egusphere-egu23-14208, 2023.