CR2.7

CR2 EDI
From climate to ice core proxy signal and reverse – primary and secondary signal formation processes 

Ice cores are a crucial archive to study past climates, containing various proxies which provide insights into the variability of atmospheric circulation and composition, past temperatures, volcanic activity, biological production and sea ice extent on different timescales. The accuracy and reliability of reconstructed climate parameters, however, depends on a detailed understanding of the processes forming the proxy signal. Relevant processes might not be the same throughout time, and could be variable on a spatial scale, i.e. different for ice core sites in Antarctica, Greenland, Svalbard or high alpine areas. In light of new projects that will analyse very old ice (e.g. Beyond EPICA Oldest Ice), it is even more important to understand the archival of climatic signals in proxies, such as stable water isotopes, impurities, dust, tephra, gases and trace elements in order to develop suitable methods for the recovery of the original climate signal.

This session intends to foster cross-disciplinary exchanges of paleoclimatologists working on established and novel climate proxies in ice cores and their interpretation. We welcome contributions that investigate the transfer function between climate and ice core proxies describing both the primary climatic imprint at the surface and potential secondary, post-depositional modifications of proxy records. We invite submissions from, but not limited to, field studies and lab experiments on the primary signal formation, theoretical simulations and proxy system modeling, as well as studies investigating the role of secondary processes modifying the original climate signal, and methodologies to optimally retrieve information from disrupted or altered proxy records (e.g. through melt events, transport and diffusion). We further encourage submissions presenting novel statistical methods, model-based studies and potential geochemical proxies.

Convener: Alexandra ZuhrECSECS | Co-conveners: Sonja WahlECSECS, Eric Wolff, Federico ScotoECSECS, Fabrice Lambert
Presentations
| Tue, 24 May, 11:05–11:40 (CEST), 13:20–14:42 (CEST)
 
Room 1.15/16

Presentations: Tue, 24 May | Room 1.15/16

Chairpersons: Alexandra Zuhr, Sonja Wahl
11:05–11:10
11:10–11:16
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EGU22-3462
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ECS
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On-site presentation
Dorothea Elisabeth Moser, Johannes Freitag, and Elizabeth R. Thomas

Coastal low-elevation ice caps of the (Ant-)Arctic and mountain glaciers are at the forefront of climate change. Retrieving ice core records from these regions is crucial to assess current, and predict future, environmental changes.  However, climate reconstruction from melt-affected ice cores is challenging. It requires a comprehensive understanding of the site-specific, near-surface melt conditions, which are fundamental to consequent melt-induced alteration of climate proxies.

Here, we use core-scale microfocus X-ray computer tomography to investigate melt layer microstructure in firn core sections from three (sub-)Antarctic sites (Young Island, Smyley Island, and Sherman Island) at 120-µm resolution. We present density, pore and grain cluster size of 3D melt features and discuss how the secondary imprint of the melt-refreeze process is visible in firn microstructure. We further show that the appearance of melt features varies both within profiles and from site to site. Given that local climate drives the near-surface snow properties and melt conditions, we suggest that melt layer microstructure could be further developed as a useful climate proxy itself.

How to cite: Moser, D. E., Freitag, J., and Thomas, E. R.: Insights from 3D Firn Microstructure into Near-Surface Snow Melt Conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3462, https://doi.org/10.5194/egusphere-egu22-3462, 2022.

11:16–11:22
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EGU22-10784
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ECS
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On-site presentation
Veronica Tsibulskaya and Jean-Louis Tison

The fabric and texture evolution with depth was investigated on several firn/ice cores from ice rises on Princess Ragnhild Coast, East Antarctica. Results at 5 m sampling resolution show important variations in the crystal orientation fabrics as well as in the grain size, on centimetric to decimetric scale. Further analysis on continuous sections spanning several meters of firn core brings to light periodic variations in the fabric clustering. The fabric’s decimetre-scale periodicity displays a clear correlation with the seasonal variability of δ18O and ECM conductivity in the ice. It also reveals a previously unobserved fabric shape. This constitutes an opportunity for a close-up look of the climatic signal burial through the transition from firn to ice.

How to cite: Tsibulskaya, V. and Tison, J.-L.: Ice fabrics and textures in coastal East Antarctica reveal seasonal variations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10784, https://doi.org/10.5194/egusphere-egu22-10784, 2022.

11:22–11:28
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EGU22-12025
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ECS
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Virtual presentation
Yuzhen Yan, Michael Bender, and John Higgins

Ice cores offer a unique opportunity to study past atmospheric composition because the trapped gases are ultimately derived from ancient atmosphere. This distinctive ability has motivated some pioneering efforts in the late 1980s to measure the elemental composition of the trapped air. The goal at that time was to reconstruct past atmospheric O2 concentration variations (PO2), the primary (atmospheric) signal. However, these measurements quickly revealed that oxygen, argon, and nitrogen concentrations in the ice (expressed as δO2/N2 and δAr/N2) are altered by gas-trapping processes. This is the secondary (and confounding) signal formation process.

Such alterations have long thwarted the application of ice core δO2/N2 to reconstruct true PO2. Empirically though, δO2/N2 in the trapped air has a high coherency with local summer insolation, but the cause is not well understood. Presumably, the intensity of sunlight on the surface of the ice sheet determines the extent and nature of snow metamorphism, which in turn modulates the magnitude of O2 and Ar losses relative to N2 at the “bubble close-off depth” (typically 70-120 m in polar regions).

Here, we discuss recent efforts to identify the secondary signals in δO2/N2 and extract the primary, atmospheric PO2 signals. First, using δAr/N2 as a proxy for insolation, we show that PO2 remained stable prior to the Mid-Pleistocene Transition (MPT), the shift from 40- to 100-kyr glacial cycles. After the MPT, however, PO2 began to decline, possibly linked to enhanced to weathering as a result of glacier expansion and, to a lesser degree, more exposed areas of the continental shelves.

Next, we proceed to exploit the secondary signal itself. That is, δO2/N2 and δAr/N2 could be used as a direct proxy of local insolation. By examining the relationship between elemental ratios and temperature proxies, we explore the relationship between high-latitude southern hemisphere insolation and Antarctic temperature in three time slices in the Pleistocene. The implications for the nature of 40-kyr glacial cycles will be discussed.

How to cite: Yan, Y., Bender, M., and Higgins, J.: Oxygen in the trapped air: identifying primary atmospheric signals and secondary bubble close-off fractionation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12025, https://doi.org/10.5194/egusphere-egu22-12025, 2022.

11:28–11:34
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EGU22-2266
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ECS
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On-site presentation
Anja Beschnitt, Johanna Schäfer, Margit Schwikowski, and Thorsten Hoffmann

Ice cores are valuable climate archives preserving organic compounds from atmospheric aerosols over long time ranges. Different approaches of dating are available like annual layer counting, radioactive decay and stratigraphic markers like tephra from volcanic eruption. In combination, they enable accurate dating back to 800,000 years. Secondary organic aerosols (SOA) are formed in the atmosphere by condensation of oxidized highly volatile organic compounds and their chemical profile is highly complex due to the variety of emission sources and reactions in the atmosphere.

Well-known SOA markers include pinic acid, pinonic acid or terebic acid from monoterpene oxidation. Another class of important atmospheric markers are biomass burning products. During combustion of cellulose levoglucosan, an anhydrosugar is formed while the combustion of lignin results in the formation of phenolic compounds like vanillic acid, cinnamic acid, or p-hydroxybenzoic acid. While the lignin burning products provide important information on paleo-fire history, intact polymeric lignin offers a deeper insight into the type and abundance of vegetation. By alkaline oxidation, the polymeric lignin is degraded into the lignin oxidation products (LOP) and the ratios of these products are related to wooden and non-wooden, as well as angiosperm and gymnosperm vegetation.

In this work, an analytical approach is presented covering a variety of SOA markers, biomass burning markers, and polymeric lignin, using UHPLC-HRMS and an elaborate sample preparation procedure. The method was applied to samples from Colle Gnifetti in the Swiss-Italian Alps, a part of Grenzgletscher, covering the time between 1920 and 1994. We present first data on polymeric lignin in ice core samples and an examination of correlations with known organic proxies to emphasize the relevance of lignin not only in climate archives like speleothems and sediments but also in ice core samples.

How to cite: Beschnitt, A., Schäfer, J., Schwikowski, M., and Hoffmann, T.: Trace analysis of organic aerosol markers and lignin in samples from Alpine ice core Colle Gnifetti covering the 20th century using UHPLC-HRMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2266, https://doi.org/10.5194/egusphere-egu22-2266, 2022.

11:34–11:40
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EGU22-8235
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Presentation form not yet defined
Changes of ammonia and nitrogen oxide emissions in South-eastern Europe inferred from an Elbrus (Caucasus, Russia) ice core record (1774-2009 CE)
(withdrawn)
Michel Legrand, Mstislav Vorobyev, Daria Bokuchava, Aleksandra Khairedinova, Stanislav Kutuzov, Vladimir Mikhalenko, Maria Vinogradova, Andreas Plach, Andreas Stohl, Patrick Ginot, Sabine Eckhardt, and Susanne Preunkert
Lunch break
Chairpersons: Federico Scoto, Alexandra Zuhr
13:20–13:26
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EGU22-4492
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On-site presentation
Pascal Bohleber, Nicolas Stoll, Barbara Delmonte, Marcello Pelillo, Marco Roman, Kaleem Siddiqi, Barbara Stenni, Sebastiano Vascon, Ilka Weikusat, and Carlo Barbante

Identifying, understanding, and constraining post-depositional processes altering the original layer sequence in ice cores is especially needed in order to avoid misinterpretation of the oldest and most highly thinned layers. The record of soluble and insoluble impurities represents an important part of the paleoclimate proxy set in ice cores but is known to be affected post-depositionally through interaction with the ice matrix, diffusion and chemical reactions. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been recognized for its micron-scale resolution and micro-destructiveness in ice core impurity analysis. Important added value comes from employing LA-ICP-MS for state-of-the-art 2D chemical imaging. The latter has already revealed a close relationship between the ice grain boundary network and impurity signals with a significant soluble component, such as Na. Here we show the latest improvements in 2D chemical imaging of ice with LA-ICP-MS, by increasing the spatial resolution from 35 to 20 and even 10 µm and extending the simultaneous analysis to cover also mostly insoluble impurity species, such as Al. The latter reveal clear signals of insoluble particle aggregates in samples of Greenland ice cores. Combining the chemical images with computer vision-based image analysis allows to separate the geochemical signals of grain boundaries and insoluble particles. Considering intensities as well as elemental ratios, this classification further highlights important differences in the geochemical signals depending on the location of the impurities in the ice matrix. Ultimately, we discuss how this refined approach may serve to investigate post-depositional changes occurring with increasing depth to the soluble and insoluble impurity components, based on grain growth and chemical reactions, respectively.

How to cite: Bohleber, P., Stoll, N., Delmonte, B., Pelillo, M., Roman, M., Siddiqi, K., Stenni, B., Vascon, S., Weikusat, I., and Barbante, C.: Glacio-chemical signature of grain boundaries and insoluble particle aggregates in ice core 2D impurity imaging, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4492, https://doi.org/10.5194/egusphere-egu22-4492, 2022.

13:26–13:32
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EGU22-5031
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Presentation form not yet defined
Barbara Delmonte, Giovanni Baccolo, Valter Maggi, and Massimo Frezzotti

Mineral dust archived in polar ice cores can be used to document past atmospheric circulation variability and past climate conditions over the dust source areas. Thanks to its relative immobility and stability, eolian dust concentration has been used to synchronize deep ice cores as well as ice stratigraphies and marine sediment records. However, mineral impurities in deep ice can be affected by post-depositional physical and chemical alterations, deriving from small-scale relocation of dust grains and subsequent alteration in acidic micro-environments.

By applying a set of different techniques spanning from dust concentration and grain size to iron mineralogy and elemental composition, here we provide evidence of in situ dust physical and chemical alterations observed below 1000 m depth in the 1620-m deep TALDICE ice core drilled at Talos Dome (peripheral East Antarctica, 72°49’S, 159°11’E; 2315 m a.s.l.). Results highlight significant dust aggregation and alteration of Fe-minerals with englacial precipitation of neo-formed jarosite, occurring in parallel with the decline of ferrous minerals and depletion of some major elements. Therefore, below 1000 m depth the TALDICE dust record can be considered partly affected by acidic-oxidative weathering resulting from the interaction of dust particles with highly saline acidic brines. Although limited to only one specific site, this study opens new issues concerning the interpretation of climate signals in the deepest part of ice cores.

How to cite: Delmonte, B., Baccolo, G., Maggi, V., and Frezzotti, M.: Deep ice and mineral dust: the case of the TALDICE ice core, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5031, https://doi.org/10.5194/egusphere-egu22-5031, 2022.

13:32–13:38
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EGU22-2255
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ECS
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Virtual presentation
Giuditta Celli, Warren R.L. Cairns, Joel Savarino, Barbara Stenni, Massimo Frezzotti, Niccolò Maffezzoli, Clara Turetta, Claudio Scarchilli, Barbara Delmonte, Rita Traversi, and Andrea Spolaor

Sunlit snow is highly photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Bromine (Br), Iodine (I) and Mercury (Hg) can be photoactivated by the UV radiation and, in certain circumstances, released from the snowpack into the atmosphere. Mercury is a heavy metal with a known toxicity present in the environment in several different chemical forms. Once present in the snowpack, Hg is very labile and, thanks to the UV light, it can be reduced back to elemental Hg (Hg(0)) and undergo dynamic exchange with the atmosphere. Similar to mercury, iodine can undergo photochemical activation in surface snow resulting in its presence in the surrounding atmosphere where it plays a crucial role in new particle formation. Bromine  has a central role in the mercury cycle in polar regions (through the Atmospheric mercury depletion events) as well as contributing to the tropospheric ozone cycle in the polar region causing the so-called Ozone depletion events. However, compared to Iodine and Mercury, it seems to be more stable after deposition into the snow pack. 

Here we present measurements of bromine, iodine and mercury performed by ICP-MS, on snow pit and shallow core samples taken over a 2100 km traverse in East Antarctica from the coast to the interior (Talos Dome – Dome C traverse 2016 and East Antarctic International Ice Sheet Traverse, EAIIST 2019). The shallow core and the snow pit samples at each site are estimated to cover about 10 to 20 years of snow accumulation, giving us a deposition record from approximately the late 90s, to around the early 21st century. The concentrations determined in different  sampling sites show a rather clear decrease trend from the coast with the minima as we approach the inner part of the Antarctic plateau. In addition, the analysis of surface and bulk samples from EAIIST show a decrease of concentrations toward the inland except for the sites characterised by a strong snow metamorphosis caused mainly by the wind friction. In almost all the sampling sites of the EAIIST traverse the concentrations of Br, I and Hg increase with sample depth, possibly due to snowpack photochemical activation in the upper part of the snowpack. Future studies are planned to  investigate the possible link between the determined concentration profile and the variation of the solar radiation reaching the Antarctic Plateau during spring caused by the ozone hole formation. 

How to cite: Celli, G., Cairns, W. R. L., Savarino, J., Stenni, B., Frezzotti, M., Maffezzoli, N., Turetta, C., Scarchilli, C., Delmonte, B., Traversi, R., and Spolaor, A.: Bromine, Iodine and Mercury on the East Antarctic plateau: preliminary results from sampling along a traverse. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2255, https://doi.org/10.5194/egusphere-egu22-2255, 2022.

13:38–13:44
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EGU22-5683
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ECS
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Virtual presentation
Delia Segato, Elizabeth R. Thomas, Amy King, Dieter Tetzner, Dorothea Elisabeth Moser, Clara Turetta, Alfonso Saiz-Lopez, Bradley Markle, Joel Pedro, and Andrea Spolaor

Over the last four decades, the Southern Ocean has been characterized by now-persistent stronger westerly winds, with consequences for the Antarctic region climate, including variations in sea ice extent and primary productivity. Here we present the first ever bromine, sodium and iodine records, tracers of sea salt aerosols, sea ice and primary productivity, from five sub-Antarctic ice cores, retrieved from Bouvet, Young, Peter I and Mount Siple Island and Mertz glacier. The aim of the study is (1) to assess if halogens deposited in sub-Antarctic regions are influenced by recent changes in wind forcing and (2) to better understand the underlying processes of halogens emission from ocean/sea ice, their transport and deposition over the Antarctic region.

The trends of sodium and bromine, emitted and transported with sea salt aerosols, suggest that wind strengthening leads to more halogens deposited in the sub-Antarctic. Also, we find that bromine is depleted with respect to the bromine-to-sodium sea-water ratio at all sites, indicating that bromine species are sustained in the marine boundary layer by halogen chemistry and are less prone to be deposited. Iodine records show a positive correlation with marginal sea ice and primary productivity variability, suggesting that iodine species emitted at the edge are deposited more efficiently than bromine species.

How to cite: Segato, D., Thomas, E. R., King, A., Tetzner, D., Moser, D. E., Turetta, C., Saiz-Lopez, A., Markle, B., Pedro, J., and Spolaor, A.: Halogens in sub-Antarctic ice cores modulated by wind forcing, sea ice and primary productivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5683, https://doi.org/10.5194/egusphere-egu22-5683, 2022.

13:44–13:50
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EGU22-9900
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ECS
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On-site presentation
Elena Di Stefano, Giovanni Baccolo, Paolo Gabrielli, Barbara Delmonte, and Valter Maggi

Antarctic ice cores play a central role in paleoclimatic reconstructions, as they provide a high resolution archive of past climatic and environmental processes. This study focuses on the TALDICE ice core drilled at Talos Dome (East Antarctica, 72°49’S, 159°11’E), which covers more than 343k years of climate history. A comparison is presented between samples analyzed through two different techniques: low background instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-SFMS). While the former is used to investigate only the insoluble fraction of dust, as it can only be applied to solid samples, the latter is used to assess the elemental composition of both the total and the soluble fraction of dust. We thus observe how different elements partition between soluble and insoluble phase at different depths of the ice core and link the geochemical patterns of the considered elements to the main climatic oscillations covered in the Talos Dome ice core.

We determined 45 elements through ICP-SFMS and 39 through INAA, with a good overlapping of the elements between the two techniques. Besides the determination of major elements (Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe), which is important in the assessment of the impact of dust on the ecosystem (e.g. source of nutrients in the Southern Ocean), the high sensibility of both techniques also permitted the determination of trace elements. Among these, rare earth elements (REE) are of particular importance as they have been widely used as a geochemical tracer of aeolian dust sources.

We present enrichment factors and correlation matrices to assess the crustal or non-crustal origin of the considered elements. The high correlations and low enrichment factors found among insoluble elements confirm a prevalent crustal composition for mineral dust. Regarding solubility, the majority of elements exhibits a minimum in solubility during the last glacial maximum. This is the result of higher fluxes of mineral dust transported to the Antarctic continent during cold climate periods and is consistent with the crustal origin we documented for most of the elements considered.

 

 

How to cite: Di Stefano, E., Baccolo, G., Gabrielli, P., Delmonte, B., and Maggi, V.: Analysis of impurities from Talos Dome ice core to assess the solubility of different elements  using INAA and ICP-SFMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9900, https://doi.org/10.5194/egusphere-egu22-9900, 2022.

13:50–13:56
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EGU22-6818
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ECS
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On-site presentation
Giyoon Lee, Jinho Ahn, Hyeontae Ju, Florian Ritterbusch, Ikumi Oyabu, Christo Buizert, Songyi Kim, Jangil Moon, Sambit Ghosh, Kenji Kawamura, Zheng-Tian Lu, Sangbum Hong, Chang Hee Han, Soon Do Hur, Wei Jiang, and Guo-Min Yang

Ice coring in blue ice areas (BIAs) serves as an alternative to deep ice core drilling, allowing collection of large-sized old ice samples in a cost-effective way because old ice samples are outcropped to the surface. However, the stratigraphy in many blue ice areas can be complicated due to complex ice flows. Based on ice layers defined by dust bands and ground penetration radar (GPR) surveys, we show that Larsen BIA has a surface transect of ice with an undisturbed horizontal stratigraphy from mid- to downstream side ice. However, the upstream ice exhibits a potential repetition of ages on scales of tens of meters. Correlating δ18Oice, δ18Oatm, and CH­4 records of Larsen ice with existing ice core records indicates that the analyzed gas age and ice age ranges between 9.2–23.4 ka BP and 5.6–24.7 ka BP, respectively. Radiometric 81Kr dating of one of the cores confirms the estimated gas ages within uncertainty. A tentative reconstruction based on a simple analytical framework suggests a warming of 15 ± 5 ℃ during the last deglaciation that we attribute to the retreat of the Ross Ice Shelf, and an increase in snow accumulation by a factor of 1.7–4.6 that we attribute to the increased penetration of snow-bearing storms. Exact estimation of the original deposition site and updated ice ages may enhance the tentative climate reconstructions in future studies. Our study shows that BIAs in Northern Victoria Land may contribute to obtain high-quality paleoclimate proxy records through the last deglaciation.

How to cite: Lee, G., Ahn, J., Ju, H., Ritterbusch, F., Oyabu, I., Buizert, C., Kim, S., Moon, J., Ghosh, S., Kawamura, K., Lu, Z.-T., Hong, S., Han, C. H., Hur, S. D., Jiang, W., and Yang, G.-M.: Chronostratigraphy of Larsen blue ice, East Antarctica, and a tentative reconstruction of surface temperature and accumulation rate during the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6818, https://doi.org/10.5194/egusphere-egu22-6818, 2022.

13:56–14:02
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EGU22-4226
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ECS
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On-site presentation
Eirini Malegiannaki, Vasileios Gkinis, Carlo Barbante, and Dorthe Dahl-Jensen

The Beyond EPICA project for retrieving the Oldest Ice Core (1.5 Myr) in Antarctica aims at obtaining high resolution climate records and water isotopes will be one of the most important parameters investigated. Given the extremely thin nature of the annual ice core layers, as we get deep down to the core, analysis of such an ice core requires new adopted techniques on water isotopes with high accuracy and precision. Laser ablation (LA) is an established powerful technique used in various fields and it can also be applied in ice sampling serving a dual purpose: a.direct solid-gas transition and b. the smallest amount of sample possible is used for analysis and that makes LA a micro-distructive process. A new instrument which couples LA sampling with the established Cavity Ring Down Spectroscopy (CRDS) for water isotopic analysis is developed. This novel design will allow both fast gas phase sample collection directly from the ice sample and high quality water isotopic measurements. Particular focus was given in the LA system which consists of a High Energy femtosecond IR LASER and the optical elements that focus the LASER beam into the ice surface. The focusing lens system is placed inside a freezer, up above a motorized stage that accomodates the ice sample. An enclosure supplied with dry air flow was build around the optics and tested by the means of humidity experiments. Subsequent series of experiments with varying laser ablation parameters: pulse energy, repetition rate, ablation time, together with the ablated crater characterization allow the evaluation of LA efficiency in ice and thus the optimization of the parameters controlling the ablation mechanism. Understanding the LA mechanism will provide the knowledge to further develop the sampling procedure and efficiently control and guide the vaporized ice into a CRDS instrument for detection.

How to cite: Malegiannaki, E., Gkinis, V., Barbante, C., and Dahl-Jensen, D.: Optimization of ’cold’ laser ablation sampling for water isotopic analysis on ice cores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4226, https://doi.org/10.5194/egusphere-egu22-4226, 2022.

14:02–14:12
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EGU22-13161
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ECS
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solicited
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Highlight
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On-site presentation
Mathieu Casado, Alexandra Zuhr, Amaëlle Landais, Ghislain Picard, Laurent Arnaud, Giuliano Dreossi, Barbara Stenni, and Frederic Prié

Water isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic  composition. Using excess parameters (combining dD, d17O, and d18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.

How to cite: Casado, M., Zuhr, A., Landais, A., Picard, G., Arnaud, L., Dreossi, G., Stenni, B., and Prié, F.: Water Isotopic Signature of Surface Snow Metamorphism in Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13161, https://doi.org/10.5194/egusphere-egu22-13161, 2022.

14:12–14:18
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EGU22-7601
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ECS
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On-site presentation
Sonja Wahl, Hans Christian Steen-Larsen, Abigail G. Hughes, Alexandra Zuhr, Anne-Katrine Faber, Tyler R. Jones, Laura J. Dietrich, Melanie Behrens, Joachim Reuder, and Maria Hörhold

Observed variability in summer surface snow isotopic composition (δ18O, δD) cannot solely be explained by precipitation events. This variability however, influences the overall summer isotope signal that is archived in ice cores. It is therefore important to explain the origin of such post-depositional modifications of the snow isotope signal to ensure an optimal interpretation of ice core isotope records. The continuous exchange of humidity between the atmospheric vapor reservoir and the snow surface through sublimation and deposition could be a key process. Yet, in the past, the surface humidity flux has been disregarded as influential for the formation of the isotope signal in snow based on the assumption of the absence of isotopic fractionation during sublimation. Here we show evidence of isotopic fractionation during snow sublimation through a combination of laboratory experiments, in-situ observations from the Greenland Ice Sheet, and snow surface modeling. We document substantial isotopic enrichment in the uppermost centimeters of snow induced by sublimation and find that the in-situ observed summer season temporal evolution of the snow surface isotopic composition (in between precipitation events) can be attributed to surface humidity fluxes. We further discuss the nature and the underlying physical process of fractionation during sublimation. Our results lead to an improved process understanding and necessitate the implementation of fractionation during the sublimation process in isotope-enabled climate models.

How to cite: Wahl, S., Steen-Larsen, H. C., Hughes, A. G., Zuhr, A., Faber, A.-K., Jones, T. R., Dietrich, L. J., Behrens, M., Reuder, J., and Hörhold, M.: Snow surface water isotope variability driven by vapor-snow exchange, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7601, https://doi.org/10.5194/egusphere-egu22-7601, 2022.

14:18–14:24
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EGU22-10188
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ECS
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On-site presentation
Alexandra Zuhr, Amaëlle Landais, Mathieu Casado, Bénédicte Minster, Frederic Prié, Romilly Harris-Stuart, Ghislain Picard, Laurent Arnaud, Marie Dumont, Inès Ollivier, and Thomas Laepple

The isotopic composition (d18O, dD) of surface snow on an ice sheet is primarily seen as a recorder of the air temperature and is used to reconstruct past climatic conditions from ice cores. The second order parameters d-excess and 17O-excess can preserve climatic signals from the moisture origin and are indicative for kinetic fractionation processes in the water cycle between the source and the deposition site. Fractionation is especially important for the surface snow which can exposed to the atmosphere for a long time during periods without snowfall. The resulting effect of this process on the isotopic composition and the second order parameters in the interior of Antarctica is, however, unclear. In order to better understand the contribution of secondary processes on the isotopic signature and to disentangle the climate characteristics at the moisture source region and at the ice core site, we study both the isotopic composition and the second order parameters of surface and subsurface snow at Dome C on the East Antarctic Plateau. For this, we make use of an extensive data set of isotopic data (d18O, dD, dexcess and 17O-excess) from surface (0 - 1.5 cm) and subsurface snow (1.5 - 4.5 cm) covering continuously the period from 2016 to 2020. This data set is complemented with previously published isotopic data of surface snow and precipitation data back to 2011. For additional comparisons and analyses, we use data from a nearby weather station, the ERA5 reanalysis data set, a satellite-derived grain index estimate and simulations from the detailed snowpack model CROCUS.

We observe a good (weak) correlation between the ambient temperature and the surface (subsurface) layer. Most years are characterised by a strong increase in the isotopic composition towards the summer and a gentle decrease towards winter while d-excess shows a contrary behaviour. We suggest that the strength of the summer increase is related to the amount of precipitation and the magnitude of metamorphism at the surface. The degree of metamorphism can (to some degree) be approximated from observational data (e.g. the grain index) or from model output (e.g. latent heat flux from CROCUS). In addition to presenting possible mechanisms leading to strong or weak increases in the isotopic composition in summer, we developed a simple model using temperature and snowfall data from ERA5 to analyse the contribution of temperature and other parameters to the observed isotopic signals.

How to cite: Zuhr, A., Landais, A., Casado, M., Minster, B., Prié, F., Harris-Stuart, R., Picard, G., Arnaud, L., Dumont, M., Ollivier, I., and Laepple, T.: What is driving the isotopic composition of surface snow in East Antarctica? - Insights from a multi-year time series of surface snow at Dome C, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10188, https://doi.org/10.5194/egusphere-egu22-10188, 2022.

14:24–14:30
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EGU22-6443
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Presentation form not yet defined
Vasileios Gkinis, Thomas Laepple, Eirini Malegiannaki, and Fyntan Shaw

The recently commenced drilling operation at the Beyond EPICA Little Dome C (BELDC) site will attempt to recover an ice core that reaches back to 1.5 Ma, a time during which the enigmatic Mid-Pleistocene Transition (MPT) took place. While the ice flow and heat flux regime at the drilling site will largely determine the age, as well as the nominal temporal resolution of the deeper parts of the BELDC core, molecular diffusion in solid ice will play a significant role in the effective temporal resolution of the δ18O signal. Here we look into the expected diffusion characteristics of the BELDC ice core by firstly addressing a previously reported problem, that of the δ18O signal loss in the deeper parts of the Dome-C ice core, particularly over Marine Isotope Stage 19 (MIS-19). By using isotope diffusion modelling in combination with high resolution δ18O data, we show the importance of the ice flow thinning function for the estimation of the diffusion length. We also comment on the large uncertainty imposed by the poor knowledge of the diffusivity coefficient. Based on recently published results on the dating of the BELDC site we provide a first order estimate of the effective resolution of the δ18O signal over the MPT transition.

How to cite: Gkinis, V., Laepple, T., Malegiannaki, E., and Shaw, F.: The problem of signal loss for the upcoming Beyond EPICA Little Dome C (BELDC) ice core., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6443, https://doi.org/10.5194/egusphere-egu22-6443, 2022.

14:30–14:36
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EGU22-5847
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ECS
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Virtual presentation
Sentia Goursaud Oger, Louise Sime, and Max Holloway

The historical period  (from 1850 to present) yields a window when ice core  and good historical data are both available. It thus represents an important period over which to test the relationship between ice core measurements, here stable water isotopes, and Antarctic climate.  Water stable isotopes from ice cores from Antarctica have traditionally been used to infer past surface air temperatures. Here we run an ensemble over the period 1850-2004 using the UK Met Office HadCM3 general circulation model equipped with water stable isotopes.  Simulations of water stable istopes from general circulation model can help in the interpretation of Antarctic ice cores.  This ensemble captures observed temperature and precipitation trends. Interestingly however the water isotopes exhibit little trend. This appears to be explained by compensating effect of two modes of atmospheric dynamics throughout the period. Further we use these results to examine the relationships used in Last Millienium reconstructions based on Antarctic stable water isotopes data from ice cores.  

How to cite: Goursaud Oger, S., Sime, L., and Holloway, M.: Insights from the first analysis of Antarctic water stable isotope simulations for the historical period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5847, https://doi.org/10.5194/egusphere-egu22-5847, 2022.

14:36–14:42
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EGU22-8361
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On-site presentation
Marina Duetsch, Peter N. Blossey, Andrew G. Pauling, and Eric J. Steig

The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132,000 and 116,000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation and ocean surface conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conducted high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, using boundary conditions provided by climate-model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include lower δ18O at Mount Moulton Blue Ice Area and higher δ18O at SkyTrain Ice Rise in West Antarctica, and higher deuterium excess at Hercules Dome, East Antarctica. A combination of records from multiple sites would provide the strongest constraint on the timing and magnitude of past WAIS collapse.

How to cite: Duetsch, M., Blossey, P. N., Pauling, A. G., and Steig, E. J.: Response of water isotopes in precipitation to a collapse of the West Antarctic Ice Sheet in high resolution simulations with the Weather Research and Forecasting and Community Atmosphere Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8361, https://doi.org/10.5194/egusphere-egu22-8361, 2022.