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EDI
The state-of-the-art in ice coring sciences

The half-century since the first deep ice core drilling at Camp Century, Greenland, has seen extensive innovation in methods of ice sample extraction, analysis and interpretation. Ice core sciences include isotopic diffusion analysis, multiple-isotope systematics, trace gases and their isotopic compositions, ice structure and physical properties, high-resolution analysis of major and trace impurities, and studies of DNA and radiochemistry in ice, among many others. Many climate and geochemical proxies have been identified from ice cores, with ongoing effort to extend their application and refine their interpretation. Great challenges remain in the field of ice coring sciences, including the identification of suitable sites for recovery of million-year-old ice; spatial integration of climate records (e.g. PAGES groups Antarctica2k and Iso2k); and deeper understanding of glaciological phenomena such as streaming flow, folding of layers and basal ice properties. This session welcomes all contributions reporting the state-of-the-art in ice coring sciences, including drilling and processing, dating, analytical techniques, results and interpretations of ice core records from polar ice sheets and mid- and low-latitude glaciers, remote and autonomous methods of surveying ice stratigraphy, and related modelling research.

Convener: Michael DyonisiusECSECS | Co-conveners: Michael DöringECSECS, Julien WesthoffECSECS, Amy KingECSECS, Anja Eichler
Presentations
| Thu, 26 May, 11:05–11:47 (CEST), 13:20–14:48 (CEST)
 
Room 0.14

Thu, 26 May, 10:20–11:50

Chairpersons: Michael Dyonisius, Michael Döring, Amy King

11:05–11:11
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EGU22-5434
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On-site presentation
Zoltán Kern and Aurel Perșoiu

Since the first core drilled in a cave ice deposit in 1947, more than 141 m of ice cores has been extracted from 20 cave ice deposits worldwide until 2021. Cave ice drilling projects focused mainly in Central European caves, however, half of the cave ice cores (3 out of 6) published in 2020 represent non-European localities predicts that an increasing number of such projects are focusing on other geographical areas hosting ice caves. Depending on the two types of ice encountered (firnified snow and frozen water), local climatic conditions and cave geometry, cave ice cores have highly variable length (between 1 and 25 m long), time span and continuity of the record covered (from a few years up to several thousands of year). The longest cave ice core in terms of both core length (~25 m) and continuous time span (~10 kyr) comes from Scărișoara Ice Cave (Romania), with several others (in Spain, Slovakia, Austria, Romania, the USA) reaching back in time towards (and beyond) the mid-Holocene. Major challenges in cave ice core science are posed by 1) presence of englacial rocky and woody debris, 2) complex stratigraphy of the ice deposits (often disturbed due to ice flow in a restricted space), 3) problematic chronology and 4) complex mechanisms of climate-proxy information transfer. Regardless, cave ice deposits offered over the past decade several unique records of Holocene climate and environmental change as well as of past microbial and fungal diversity. Because ice caves are located at much lower altitudes and latitudes than polar and mountain glaciers, they face the double threat of both increasing temperatures and precipitation amounts, several possible milennial old deposits being lost over the past few years. An ongoing race to salvage the paleoclimatic information these ice deposits holds is thwarted by climatic, financial and knowledge risks.

How to cite: Kern, Z. and Perșoiu, A.: The state-of-the-art in cave ice coring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5434, https://doi.org/10.5194/egusphere-egu22-5434, 2022.

11:11–11:17
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EGU22-8040
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ECS
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On-site presentation
Carla Huber et al.

High-alpine glacier ice cores are useful natural archives and allow access to continuous pollution records back to the pre-industrial era. This is especially true for glacier ice cores drilled in the European Alps, which are located close to the anthropogenic emission sources. However, due to global warming glaciers are increasingly affected by melting, subsequently altering the information stored in the natural archive.
Here we show the comparison between major ion records from shallow ice cores drilled on Grand Combin (4123 m a.s.l., Swiss Alps) in 2018 and 2020. Both shallow ice cores were dated applying annual layer counting using stable isotopes and concentrations of major ions (e.g., ammonium). Excellent agreement between both records was observed for the stable isotopes in the overlapping time period 2011-2018. However, in the core collected in 2020, effects of melting were detected for the major ion concentrations before 2016. As an extreme example: sulfate is significantly depleted in the years 2011-2016 in that core, losing 61% of the ion content in comparison with the core collected in 2018. Even for ammonium, which is the most preserved with only 16 % reduction, the seasonal cycle disappeared. The elution sequence matches the results of Avak et al. (2019).

Meteorological data indicate that mean annual air temperatures of 2019 and 2020 were not significantly higher than in the previous years. Instead, we attribute the melt damage in the 2020 core to a two-week period in summer 2019 with temperatures continuously above 0°C. Our finding that such a disturbance through melting can occur in only two years emphasises the critical state of these glacier archives. Thus, preserving these archives is important and a time sensitive matter.

 

REFERENCES

Avak, S. E., Trachsel, J. C., Edebeli, J., Brütsch, S., Bartels‐Rausch, T., Schneebeli, M., Schwikowski, M. and Eichler, A.: Melt‐induced fractionation of major ions and trace elements in an Alpine snowpack, Journal of Geophysical Research F: Earth Surface, 124(7), 1647-1657, https://doi.org/10.1029/2019JF005026.

How to cite: Huber, C., Eichler, A., Mattea, E., Brütsch, S., Jenk, T., Gabrieli, J., Barbante, C., and Schwikowski, M.: High-alpine Glacier Record Influenced by Melting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8040, https://doi.org/10.5194/egusphere-egu22-8040, 2022.

11:17–11:23
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EGU22-10952
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ECS
Dieter Tetzner et al.

The Southern Hemisphere Westerly Winds play a critical role in the global climate system by modulating the upwelling and the transfer of heat and carbon between the atmosphere and the ocean. Since observations started, the core of the westerly wind belt has increased in strength and has contracted towards Antarctica. It has been proposed that these deviations are among the main drivers of the observed widespread warming in West Antarctica, threatening the stability of ice shelves, and ultimately contributing to global sea level rise.

 Over the last decades, it has been widely believed these atmospheric changes have occurred in response to recently increased greenhouse gas concentrations and ozone depletion. However, the lack of long-term wind records in the Southern Hemisphere mid-latitudes hinders our ability to assess the wider context of the recently observed changes. This lack of a clear consistent timing limits our understanding of the causes of westerly wind changes and the roles they have played in driving recent environmental changes in Antarctica. Addressing these questions is crucial for future climate predictions.

 In this work, we present records of diatoms preserved in ice cores retrieved from the southern Antarctic Peninsula and the Ellsworth Land region. The diatom abundance and species assemblages from these ice cores prove to represent the regional variability in wind strength and circulation patterns that influence the onshore northerly winds. We use this novel proxy to produce an annual reconstruction of winds in the Pacific sector of the Southern Hemisphere Westerly Wind belt over the last 140 years. This wind reconstruction allows exploring the link between the recent increase in wind strength, greenhouse gases and ozone depletion in the atmosphere

How to cite: Tetzner, D., Thomas, E., and Allen, C.: Diatoms in Ice Cores, a novel proxy for reconstructing past wind variability in the Pacific sector of the Southern Hemisphere Westerly Wind belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10952, https://doi.org/10.5194/egusphere-egu22-10952, 2022.

11:23–11:29
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EGU22-9364
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ECS
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Virtual presentation
Eliza Cook et al.

We have recorded consistent (but low) numbers and a diverse range of diatom taxa (siliceous algae) over a 400-year period in the RECAP ice core, drilled from the Renland ice cap on the east coast of Greenland. This is an exciting initial step in attempting a diatom-based environmental reconstruction for an Arctic ice core for the first time, since Greenland’s inland ice cores (e.g. NGRIP, GRIP) do not appear to contain diatoms in enough numbers. Our novel study investigated the period 1528 - 1940 AD (encompassing the Little Ice Age (LIA)) and we developed a method for extracting diatom taxa from the ice-core meltwater samples for identification. This was done by microscopy using standard taxonomic techniques. In summary, the RECAP LIA assemblage comprises 93 species, 36 genera and 11 families where Thalassiosira/Coscinodiscus, Aulocoseira, Pinnularia, Nitzschia, Luticola, Diadesmis, Staurosira, Achnanthidium, Psammothidium spp are the dominant genera. In this interval we found that Renland received air blown diatoms from both planktonic/benthic freshwater (80%) and planktonic marine (20%) sources. The freshwater species included aerophilic species (from damp environments), key indicators of exposed, environments and found widely in the Arctic. We observe that both total diatom numbers and species composition changes rapidly over time (i.e. decadal timescales), similar to other ice-core proxies, and with higher total numbers/yr between about 1780 and 1850 AD. Further analysis is required to establish a link to specific environmental variables, which could include aridity, wind strength or sea ice cover. We hypothesise that similar lower altitude, coastal ice cores from Greenland and Canada could be useful diatom repositories in the Arctic region.

How to cite: Cook, E., Jones, V., and Zhu, J.: Exploring the use of diatoms as a new environmental proxy in Arctic coastal ice cores - A first case study using the RECAP ice core, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9364, https://doi.org/10.5194/egusphere-egu22-9364, 2022.

11:29–11:35
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EGU22-3916
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ECS
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On-site presentation
Jiamei Lin et al.

Large volcanic eruptions occurring in the last glacial period can be detected by their accompanying sulfuric acid deposition in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60-9 ka years before AD 2000 (b2k). Over most of the investigated interval the ice cores are synchronized making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only list Greenland sulfate depositions larger than 20 kg km-2 and Antarctic sulfate depositions larger than 10 kg km-2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 740 eruptions in Antarctica within the 51 ka period - where the sulfate deposition of 85 eruptions is found at both poles (bipolar eruptions). Based on the ratio of Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. Twenty-five of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years and 69 eruptions are estimated to have larger sulfur emission strengths than the Tambora, Indonesia eruption (1815 AD). Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16-9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. This confirms the suggestion that the isostatic unloading of the Northern Hemisphere (NH) ice sheets may be related to the enhanced NH volcanic activity. Our ice-core based volcanic sulfate records provide the atmospheric sulfate burden and estimates of climate forcing for further research on climate impact and understanding the mechanism of the Earth system.

How to cite: Lin, J., Svensson, A., S. Hvidberg, C., Lohmann, J., Kristiansen, S., Dahl-Jensen, D., Peder Steffensen, J., Olander Rasmussen, S., Cook, E., Astrid Kjær, H., M. Vinther, B., Fischer, H., Stocker, T., Sigl, M., Bigler, M., Severi, M., Traversi, R., and Mulvaney, R.: Magnitude, frequency and climate forcing of global volcanism during the last glacial period as seen in Greenland and Antarctic ice cores (60-9 ka), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3916, https://doi.org/10.5194/egusphere-egu22-3916, 2022.

11:35–11:41
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EGU22-7471
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On-site presentation
Peter Abbott et al.

Ice cores are powerful archives for reconstructing volcanism and developing tephrochronological frameworks, as they can preserve both the soluble, i.e. aerosols, and non-soluble, i.e. tephra, products of volcanic eruptions. In addition, and particularly over Holocene timescales, high-precision annually resolved chronologies have been developed for these records and permit ages to be assigned to eruptions. The identification of tephra in ice cores in direct association with chemical indicators of volcanism, such as sulphate, can significantly enhance volcanic reconstructions as tephra can be linked to an eruptive source. Such source attributions can provide information on the location of the eruptions, the magnitude of aerosol emissions at the source and help assess any climatic impact. In addition, they can aid the reconstruction of volcanic histories and the assessment of future hazard risk.  

 

The tephra record for the interior of East Antarctica over the last 5,500 years is potentially underexploited as a prior focus on visible horizons and exploring the deep ice cores that cover longer time spans has resulted in only one horizon, dated to ~3.5 ka BP, being identified in these records. Here we discuss ongoing tephrochronological investigations of two ice-cores, B53 and B54, retrieved from the interior of the East Antarctic Plateau. High-resolution, sub-annual chemical records have been measured from both cores using a continuous melter system. These data were used to develop a sampling strategy to identify cryptotephra horizons with ice-core sections containing coeval peaks in fine insoluble particles and non-sea-salt sulphur targeted and >50 events were directly sampled. This approach recently has been used to identify cryptotephras in both Greenland and Antarctic ice cores. When glass tephra shards were identified thin sections were created and individual glass shards were geochemically analysed using electron-probe microanalysis to help identify their volcanic source and permit correlations between records.

 

Thus far, more than 10 cryptotephra horizons have been identified and linked to regional sources such as the South Sandwich and South Shetland Islands and the ~3.5 ka BP event has been traced in both cores as a visible layer. More detailed investigations are being conducted on samples from specific volcanic signals of interest that may derive from eruptions of ultra-distal volcanic sources. Such eruptions could have deposited very small glass tephra shards over Antarctica, which poses significant analytical challenges and necessitates the use of innovative approaches for tephra identification and geochemical analysis.

How to cite: Abbott, P., McConnell, J., Chellman, N., Kipfstuhl, S., Hörhold, M., Freitag, J., Plunkett, G., and Sigl, M.: Mid to Late Holocene East Antarctic ice-core tephrochronology: Implications for reconstructing volcanic eruptions and their impacts over the last 5,500 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7471, https://doi.org/10.5194/egusphere-egu22-7471, 2022.

11:41–11:47
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EGU22-5470
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ECS
Francois Burgay et al.

Wildfires have an important role in affecting the Earth’s radiative balance. Biomass burning aerosols can scatter or absorb the incoming solar radiation, alter the ice and snow albedo and act as cloud condensation nuclei. Overall, their net contribution to the Earth’s radiative forcing is negative, however this estimate has large uncertainties. To better assess the impact of wildfires on climate (and vice versa), it is crucial to reconstruct their past regional and temporal variability on decadal and centennial timescales. Ice cores are excellent archives to perform such palaeofire reconstructions. Previous studies have reconstructed the occurrence of wildfires in ice cores using both inorganic (ammonium, potassium and black carbon) and organic proxies (levoglucosan, vanillic acid and p-hydroxybenzoic acid). However, a more comprehensive view that involved a broader suite of wildfire proxies was missing. Here, we present a new SPE-UHPLC-HRMS method for the determination of five organic biomass burning tracers (syringic acid, vanillic acid, vanillin, syringaldehyde and p-hydroxybenzoic acid) and pinic acid, as biogenic emission proxy, in ice core samples. This method showed average recoveries of 76% (58-88% range), excellent inter-day reproducibility, no significant matrix effects and fast analysis time (13 min per sample). Comparing the published concentration ranges of the selected species from different ice core regions (i.e. Alps, Greenland, Kamchatka, China and Svalbard Archipelago) with the procedural detection limits of this new methodology, we conclude that four of the six targeted compounds can be successfully detected in real ice and snow samples. Only for vanillin and syringaldehyde, no ice-core measurements have been reported in the scientific literature so far. The method development also involved the evaluation of common laboratory practices such as the melting and refreezing of ice samples before the analysis. We found that the melting and refreezing of the samples resulted in a mass loss for the majority of the investigated compounds, which was more evident at lower concentrations. We hypothesize that the reason of this phenomenon is the adsorption of the compounds on the walls of the glass vials used for this study. In light of this, we propose alternative sample storage strategies that can also be extended for the analysis of other compounds.

The method was successfully tested on nine ice core samples from the Colle Gnifetti (European Alps) and it will be applied on ice cores from the Alps and the Russian Altai, contributing to the better understanding of wildfire temporal evolution and their relations with climate.

How to cite: Burgay, F., Salionov, D., Huber, C., Singer, T., Ungeheuer, F., Eichler, A., Vogel, A., Bjelic, S., and Schwikowski, M.: Development and application of a novel UHPLC-HRMS method for the analysis of organic wildfire tracers in ice cores. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5470, https://doi.org/10.5194/egusphere-egu22-5470, 2022.

Thu, 26 May, 13:20–14:50

Chairpersons: Michael Dyonisius, Anja Eichler, Michael Döring

13:20–13:30
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EGU22-3584
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solicited
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Highlight
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On-site presentation
Eric Wolff and Helene Hoffmann and the WACSWAIN science team plus collaborating scientists

There is intense interest in the future stability of the West Antarctic Ice Sheet (WAIS).  Models range widely in their predictions and in the physics they include.  Because the timescales for ice sheets are long, our best hope of constraining the solutions is to look at the past behaviour of WAIS. The last interglacial (LIG) is a particularly important time because Antarctic temperature was higher than present and some models predict the complete loss of WAIS and of the large ice shelves adjacent to it.

Within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) project, in 2019 we retrieved a 651 metre ice core to the bed of Skytrain Ice Rise. This ice rise is adjacent to the Ronne Ice shelf and the WAIS, but is expected to have maintained an independent ice flow because of the protection afforded by the Ellsworth Mountains.  The ice core has been processed and analysed continuously for a range of analytes, including water isotopes, methane and major chemistry.

In this presentation we will first describe the dating of the ice core achieved in the top half of the ice column by annual layer counting supplemented by fixed horizons, and deeper down by ice flow modelling supplemented by tie points from chemistry, 10Be, as well as atmospheric CH4 and δ18O. The core is continuous through the last glacial period, and most of the last interglacial. Discontinuities occur near the base, in the ice at the older end of the LIG, so that although older ice may be  present, we can only interpret the core to 125 ka.

Overall, the ice core record shows the clearly recognisable pattern of all the Antarctic Isotopic Maxima seen in East Antarctic ice cores over the last glacial cycles. In the early part of the Holocene, we see a very interesting pattern representing thinning of the ice rise and retreat of the Ronne Ice shelf.  This allows us to add reliable dates to the history of ice retreat in the early Holocene.

In the LIG, the record of marine ions in the ice suggest that the Ronne Ice Shelf was present at least from 125 ka onwards. This rules out occurrence of some of the more extreme retreats of WAIS that would have led to seaways between the Weddell, Amundsen and Ross Seas.  We see somewhat higher water isotope ratios in the LIG than the Holocene, possibly consistent with some drawdown of WAIS in sectors other than the Weddell region.

How to cite: Wolff, E. and Hoffmann, H. and the WACSWAIN science team plus collaborating scientists: Climate of the last 125 kyr at Skytrain Ice Rise, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3584, https://doi.org/10.5194/egusphere-egu22-3584, 2022.

13:30–13:36
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EGU22-8404
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ECS
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On-site presentation
Helene Hoffmann et al.

The ice in the deepest and therefore oldest parts of polar ice cores is highly compressed. Annual layers, although potentially preserved, can be thinned to a millimeter scale or even below. However, for many palaeoclimate studies these are the most interesting sections. Within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last Interglacial) project we aim to investigate particularly the basal part of an ice core recently drilled to bedrock at the Skytrain Ice Rise in West Antarctica. Our aim is to obtain unique information on the state of the Filchner-Ronne ice shelf during the last interglacial (LIG). To achieve this we have set up a system to perform using high-resolution laser-ablation inductively coupled plasma – mass spectrometry (LA-ICP-MS) measurements using a cryocell stage on selected segments of the ice core. Here we present first results of system performance including assessment of measurement sensitivity and precision with respect to analyses of the most relevant components, including sodium, magnesium, calcium and aluminium. We report on the sample preparation technique as well as the resulting process blank. We evaluate the horizontal variability of the LA-ICP-MS signal across the ice core and the representativity of the high-resolution signal for an overall impurity content for different depth levels in the core. The results of the laser ablation ICP-MS measurements are then compared to low-resolution chemistry data from continuous flow analysis of the Skytrain ice core performed on the ice from the same depth. This comparison aims to evaluate the capabilities of the method in terms of improving depth resolution and annual variability. In a first application, sections of 80cm of ice from five different depth intervals covering time frames from late Holocene to the LIG are analysed via LA-ICP-MS and compared for their overall impurity content as well their signal variability. Finally, the potential of the method for resolving annual layers and fast changing climate signals within the core section covering the time period of the late last interglacial (about 115 - 120 ky before present) is investigated.

How to cite: Hoffmann, H., Day, J., Rhodes, R., Grieman, M., Humby, J., Rowell, I., Nehrbass-Ahles, C., Mulvaney, R., Thomas, E., Gibson, S., and Wolff, E.: Laser Ablation - ICP-MS measurements for high resolution chemical ice core analysis with a first application to an ice core from Skytrain Ice Rise (Antarctica) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8404, https://doi.org/10.5194/egusphere-egu22-8404, 2022.

13:36–13:42
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EGU22-5035
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ECS
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On-site presentation
Nicolas Stoll et al.

Impurities in polar ice play, among others, a crucial role as a proxy for the paleoclimate while at the same time impacting the internal deformation of ice on the micro-scale. In particular, solid and dissolved impurities can impact grain growth through Zener pinning or the drag of grain boundaries. Recent studies on natural ice from Antarctica and Greenland highlight the need for a multi-method approach to determine the differences in the localisation and chemistry of solid and dissolved impurities comprehensively, in order to ultimately gain a more holistic understanding. Here we report on a recent pilot investigation pursuing the direct integration of complimentary methods: microstructure-mapping, Cryo-Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with 2D impurity imaging. While LA-ICP-MS enables the fast mapping of cm-size areas with lateral resolution in the order of tens of μm, Raman spectroscopy is more suited to identify the mineralogical composition of individual solid inclusions at the single μm scale. We analysed samples from the Holocene and Last Glacial from the Northeast Greenland Ice Core Project (EGRIP) and the North Greenland Eemian Ice Drilling (NEEM) ice cores. We find that the general localisation patterns of impurities (e.g., low vs. high concentration) are similar for both methods. Furthermore, both methods show (clusters of) inclusions in the grain interior. These findings display that a holistic approach is needed to truly decipher the localisation of impurities in the ice microstructure. Combining the advantages of both methods gives a good overview of the localisation of impurities, both solid and dissolved, on the micro-scale. Localisation patterns are related to the chemistry of the analysed impurities displaying the need for high-resolution methods. For example, Na is strongly located in the grain boundaries, Al is preferentially located within the ice grains and Mg can be located in both regimes. We analyse the role of inclusions in relation to 1) their chemistry and 2) their proximity to grain boundaries. Our approach of 2D impurity imaging in concert with established techniques, such as microstructure mapping and Raman spectroscopy, provides a detailed insight into the impurity distribution throughout a broad range of depths in an ice core. We demonstrate the potential of such an approach to carefully investigate the evolution of impurity localisation in ice cores, with special significance to ice deformation processes and the preservation of the climatic record.

How to cite: Stoll, N., Bohleber, P., Hörhold, M., Erhardt, T., Eichler, J., Roman, M., Delmonte, B., Barbante, C., and Weikusat, I.: Integrating Raman spectroscopy and LA-ICP-MS 2D imaging to decipher the localisation and chemistry of impurities on the micro-scale in Greenland ice: Consistencies and open question, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5035, https://doi.org/10.5194/egusphere-egu22-5035, 2022.

13:42–13:48
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EGU22-9210
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ECS
Christoph Nehrbass-Ahles et al.

Some modelling studies and sea level reconstructions suggest the loss of the West Antarctic Ice Sheet (WAIS) during the Last Interglacial (LIG) about ~120’000 ago, but direct evidence for a collapse of the WAIS is lacking. The WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial (WACSWAIN) project aims at providing direct evidence allowing for a comprehensive assessment of whether or not the WAIS collapsed during the LIG. One of the expected consequences of such massive ice mass loss is the change of the elevation of land masses in close proximity of the WAIS due to isostatic adjustments. This process, together with changes in ice sheet thickness, may have altered the elevation of Skytrain Ice Rise above sea level on the order of 200 m. Such major changes in the elevation should be imprinted in the Total Air Content (TAC) based on simple barometric considerations. Here we present a new experimental setup of a high-accuracy, high-precision TAC measurement system constructed at the British Antarctic Survey. This setup is dedicated to and optimised for the measurement of TAC and is based on a vacuum extraction principle. The air is extracted from the ice by melting the sample by thermal radiation and the released air is dried and directly expanded into a 30-litre expansion chamber. State-of-the-art pressure gauges and thorough temperature control allow for an accuracy of 0.2% with a real ice reproducibility of 0.2% to 0.4% for 100 g and 30 g samples, respectively. Here, we discuss the performance of this new TAC system and present first TAC data from the Holocene section of the Skytrain Ice Core, Antarctica.

How to cite: Nehrbass-Ahles, C., King, A., Hoffmann, H., Grieman, M., Rowell, I., Humby, J., Miller, S., Thomas, E., Bauska, T., Schmitt, J., Mulvaney, R., and Wolff, E.: A high-accuracy Total Air Content setup: System performance and first results from Skytrain Ice Rise, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9210, https://doi.org/10.5194/egusphere-egu22-9210, 2022.

13:48–13:54
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EGU22-5914
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ECS
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Isobel Rowell et al.

Few ice cores from the Amundsen and Bellingshausen sectors of the West Antarctic Ice Sheet (WAIS) extend back in time further than a few hundred years. The WAIS is believed to be susceptible to collapse as a result of anthropogenic climate change. Modelling studies and palaeoclimatic evidence have suggested at least partial WAIS collapse and resulting sea level rise during previous warm periods, therefore understanding the stability of the WAIS during warm periods is important. The WACSWAIN project successfully drilled a 651 m ice core on Skytrain Ice Rise, adjacent to the Ronne Ice Shelf, in 2018, some data from which are now being published. The second WACSWAIN drilling project took place in 2020 on Sherman Island in the Abbott Ice Shelf, where the British Antarctic Survey’s (BAS) Rapid Access Isotope Drill (RAID) was deployed. The team drilled a 323 m deep borehole, with discrete samples of ice chippings collected from the entire depth range of the drilled ice. The samples were analysed for water isotopes and major ion content at BAS from 2020-2022. Validation of the RAID-ice data is confirmed through comparison with a shallow core drilled on Sherman Island during the same field campaign. Using annual layer counting of chemical records and volcanic horizon identification, an age scale for the record of 1724 discrete samples is presented. The Sherman Island ice record extends back to at least 1000 years before present, providing the oldest ice-derived continuous palaeoclimate record for the coastal Amundsen-Bellingshausen sector to date. An estimation of accumulation history at the site is presented. A comparison of the longer chemical and water isotope records with other regional ice cores provides insights into the spatial variability of change over recent centuries. Climate trends in the region of the Amundsen sea glaciers (including Thwaites) - considered the most vulnerable to future warming - are investigated.

How to cite: Rowell, I., Mulvaney, R., Wolff, E., Pryer, H., Tetzner, D., Thomas, L., Rix, J., and Martin, C.: 1000 years of climate history from a coastal West Antarctic ice core site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5914, https://doi.org/10.5194/egusphere-egu22-5914, 2022.

13:54–14:00
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EGU22-2075
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ECS
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On-site presentation
Amy King et al.

We present new measurements of methane (CH4) and carbon dioxide (CO2) in the Skytrain ice core, with gas ages dated around 1610AD. The aim of these measurements is to improve our understanding of why there is a significant difference between measured CO2 at that time in current ice core records.

A pronounced feature of the Law Dome record (accumulation 60 cm ice eq. yr; gas age distribution 8 years,) is a rapid decrease in CO2 of ~10 ppm over 50 years with a distinct minimum at 1610. The cause of this decrease is much debated, with complex carbon cycle feedbacks required in explanation. However, other ice cores do not show the same event. The West Antarctic Ice Sheet (WAIS) divide record (accumulation 22 cm ice eq. yr; gas age distribution 19 years) shows a steadier decline in CO2 of approximately 6 ppm over the same period, with the record also ~2-3 ppm higher than Law Dome throughout 900-1800 CE. A follow-up study using the Dronning Maud Land (DML) ice core (accumulation 7 cm ice eq. yr; gas age distribution 65 years) attempted to prove which core showed the real atmospheric signal, but results were inconclusive due to the wide gas-age distribution of the record. While Skytrain (accumulation 14 cm ice eq. yr) does not match the accumulation rate of Law Dome, we present these new, high-resolution gas measurements over the period to work towards answering the following questions: (1) if the Law Dome record is correct, what caused this amplitude of CO2 change over a short timescale? (2) Does one of the records suffer from contamination? (3) Is our understanding of gas smoothing processes in these ice cores inaccurate? We will then use these measurements, from a well-validated ‘needle-crusher’ CO2 device at the ice core labs at Oregon State University, USA, to validate a new semi-continuous ice-grating device (for which we present a preliminary outline) at the new ice core gas analysis lab at the British Antarctic Survey, UK.

How to cite: King, A., Bauska, T., Brook, E., Kalk, M., Strawson, I., Epifanio, J., Hoffman, H., and Wolff, E.: The Little Ice Age CO2 drop:  Natural, Anthropogenic or Artefact? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2075, https://doi.org/10.5194/egusphere-egu22-2075, 2022.

14:00–14:06
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EGU22-7056
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ECS
Michael Dyonisius et al.

Common methods to liberate the air bubbles trapped in ice cores include melting (wet extraction) and mechanical destruction (dry extraction) of ice under vacuum. Wet extraction is commonly used for CH4 analyses; however, a recent study (Lee et al., 2020) showed that the presence of liquid water can introduce extraneous (non-paleoatmospheric) CH4 from the reaction between the meltwater and impurities. Measurements of CH4 using dry extraction methods had previously been done (e.g., Ferretti et al., 2005); however, a laboratory intercomparison study showed that dry extraction system generally have higher blanks (Sowers et al., 1997) for CH4. It is hypothesized that friction between components (either metal with metal or metal with ice) can be a source of contamination (e.g., Nicewonger et al., 2016; Sowers et al., 1997). A third method to liberate air trapped in ice core bubbles is sublimation under vacuum (e.g., Wilson and Donahue, 1989; Schmitt et al., 2011). The sublimation method guarantees complete gas extraction from both the air bubbles and the ice matrix / clathrates (Bereiter et al., 2015), and should be free of problems associated with wet extraction. Here we present a new sublimation system that aims to sublimate ~250g of ice and extract ~25 mL STP of air for measuring CH4 isotopes in ice with high impurities. We use three high powered (500W each) infrared lamps that emit peak radiation at wavelength of 1500 nm, which coincides with a local maxima in ice absorption spectra (Warren and Brandt, 2008). To ensure even sublimation, the infrared lamps are attached to a custom-made mounting bracket that is rotated around the glass vessel. This system is coupled to a previously built Gas Chromatography Isotope Ratio Mass Spectrometry (GC-IRMS) system (Sperlich et al., 2013) to purify and analyze δ13CH4 isotopes. At the time of writing, the GC-IRMS system is able to achieve 0.06 ‰ precision on standard air injections with contemporary CH4 mole fraction (1850 nmol/mol). Further testing to characterize the performance of the system using blank ice and test ice of known mole fraction and isotope values is underway.

How to cite: Dyonisius, M., Döring, M., and Blunier, T.: ​Development of ice sublimation device for analyses of methane isotopes in ice with high impurities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7056, https://doi.org/10.5194/egusphere-egu22-7056, 2022.

14:06–14:12
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EGU22-5166
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ECS
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On-site presentation
Marie Bouchet et al.

To understand the causal relationship between forcing (orbital parameters, greenhouse gas concentration…) and the climate change, dating climate archives is crucial. Ice cores are unique archives because they provide a direct record of greenhouse gas concentration. However, dating ice cores is particular since they require two chronologies: one for the ice and one for the younger air trapped in bubbles inside the core. The coherent AICC2012 chronology was established for five ice cores: EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), North Greenland Ice core Project (NGRIP), Vostok (VK) and TALos Dome Ice CorE (TALDICE). A sedimentation model was used to reconstruct past variations of three parameters: accumulation of snow at surface, ice layer thinning in depth and Lock-In-Depth (LID), the depth where air is trapped. Ice and gas ages along the core are estimated from these parameters. Then, a Bayesian tool optimised the age scale by constraining the chronology to respect chronological observations (orbital tuning, stratigraphic links between cores, tephra layers…) and by fitting the three parameters to background scenarios (accumulation deduced from ice isotopes, LID from δ15N, …). The AICC2012 chronology is associated with an uncertainty which arises up to 6 kyrs due to the discontinuity of the ice core composition records and to the poor knowledge when it comes to choose an optimised target for orbital tuning.

Since AICC2012, many new data have been obtained to improve the ice core chronology and it is the right period to produce an updated coherent chronology which could also be extended to other ice cores. Here, we present a first step toward the construction of the next coherent ice core chronology by including new dating constraints from recent data on the EDC ice core: 1) air isotopes (δ18Oatm , δO2 /N2) and air content used as orbital dating constraints, 2) the δ15N signal used to estimate the background scenario for LID. In addition, we make use of the East Asian stalagmite δ18Ocalcite signal as an alternative synchronisation target for the δ18Oatm (Extier et al. 2018).

This new dating experiment on EDC ice core aims to lower uncertainty of the chronology while providing a critical look on former hypotheses considered to establish AICC2012. For example, δ15N record was discontinuous at the time and it has been reconstructed based on its correlation with δD. Now that we have a continuous δ15N signal, we can evaluate the relevance of this reconstruction. Following this work, we will use new tie point constraints resulting from volcanic synchronisation which has recently been undertaken between Greenland and Antarctica (Svensson et al. 2020) and the ice cores Dome Fuji and WAIS Divide will be further studied to be included in the chronology.

How to cite: Bouchet, M., Grisart, A., Landais, A., Parrenin, F., Prié, F., Raynaud, D., Lipenkov, V. Y., Capron, E., Legrain, E., Extier, T., and Svensson, A.: New dating experiment on EPICA Dome C (EDC) ice core over the last 800 kyrs using the Bayesian tool Paleochrono and new records of elemental and isotopic composition in the air trapped in the EDC ice core., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5166, https://doi.org/10.5194/egusphere-egu22-5166, 2022.

14:12–14:18
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EGU22-5519
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ECS
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On-site presentation
Fyntan Shaw et al.

The diffusion of stable water isotopes in firn and ice is a complex process which can smooth the measured isotope profile and thus remove the high frequency variations. While for the firn this process is relatively well understood and can be accounted for, this is not the case in the deepest parts of the ice core, where additional processes are introduced due to the increased temperatures near bedrock. Combined with the extreme thinning the deep ice has experienced over hundreds of thousands of years, variations up to centennial or even millennial timescales can be heavily attenuated. Understanding how to best recover this signal in the deep ice is crucial to get a reliable record in deep ice cores such as the Beyond EPICA Oldest Ice Core that is currently being drilled.

In order to reconstruct the climate signal of this old ice, an accurate estimation of the diffusion length is necessary. Current estimation methods are mostly suitable for firn and shallow ice as they are assuming a rather stationary underlying climate signal. In this contribution, we present a method which approaches the issue without assuming the low frequency climate variability is negligible. Using this method on the high-resolution Dome-C isotope data (doi.pangaea.de/10.1594/PANGAEA.939445), we provide an improved estimate of the diffusion length of the Dome-C ice-core. Both the diffusion length estimate of the deep ice in Dome-C as well as the new method are useful for the interpretation of future deep ice coring projects such as Beyond EPICA Oldest Ice Core.

How to cite: Shaw, F., Laepple, T., Kunz, T., Gkinis, V., and Dahl-Jensen, D.: Estimating the diffusion in the deepest section of the Dome-C ice core using a new statistical method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5519, https://doi.org/10.5194/egusphere-egu22-5519, 2022.

14:18–14:24
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EGU22-4760
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ECS
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On-site presentation
Antoine Grisart et al.

The EPICA Dome C (EDC) ice core has been drilled from 1996 to 2004. Its study revealed a unique 800 ka long continuous climatic record including 9 deglaciations. Ice cores contain numerous proxies in the ice and in the air trapped in bubbles (chronological constraints, greenhouse gases concentration, local temperature proxies, mid to low latitude climate proxies).

Here, we focus on the link between the high and low latitudes during the glacial/interglacial transitions provided by the isotopic composition of water and oxygen archived in both ice and gas matrix. On one hand, the water isotopic composition brings information on past temperatures and water cycle re-organizations:   dD records past temperature, whereas the combination of d18O with dD or d17O provide information on the past water cycle organization through d-excess and 17O-excess linked to climatic conditions of the evaporative regions. On the other hand, the elemental composition of oxygen expressed in the O2/N2 ratio provides key information for orbital dating over the last 800 ka in complement with the isotopic composition of atmospheric oxygen (d18O of O2 or d18Oatm) which is related as well to the low latitude water cycle.

In this study, we present new high resolution records of water isotopes of many proxies (d18O, d-excess and 17O-excess) as well as high resolution measurements of O2/N2 and d18Oatm over the last 9 deglaciations on the EDC ice core. We detail the coherent low to mid-latitude orbital patterns obtained using our multiproxy approach with a focus on Termination II, Termination V and the 800 – 500 ka. deglaciations. We look at the similar patterns between terminations and between the different proxies presented.

How to cite: Grisart, A., Landais, A., Stenni, B., Crotti, I., Legrain, E., Masson-Delmotte, V., Jouzel, J., Prié, F., Jacob, R., and Fourré, E.: Sequence of events at high resolution during deglaciations over the last 800ka from the EDC ice core, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4760, https://doi.org/10.5194/egusphere-egu22-4760, 2022.

14:24–14:30
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EGU22-4287
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ECS
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Virtual presentation
Ji-Woong Yang et al.

Global biosphere primary productivity via photosynthesis is the largest carbon uptake flux from the atmosphere. The Earth biosphere currently absorbs near half of the carbon emitted by anthropogenic activities (Friedlingstein et al., 2020). Therefore, for a better projection of future carbon cycle, it is important to understand how the global biosphere would respond to abrupt climate changes which occurred in the past. The last glacial period is punctuated by a number of rapid shifts between relatively cold (stadial) and warm (interstadial) stages named Dansgaard-Oeschger events (DO). Some stadials are also associated with abrupt, massive iceberg discharge event and are called Heinrich Stadials (HSs). The high-resolution CO2 reconstruction from polar ice cores demonstrated millennial-scale CO2 variations over HS-DO events (Bauska et al., 2021). The gradual rising of CO2 over HS has been attributed to ventilation changes in Southern Ocean (Gottschalk et al., 2016; Menviel et al., 2018) and/or reduced biological uptake (Ahn et al., 2012; Gottschalk et al., 2016; Schmittner and Lund, 2015). However, the role of the global biosphere is not well understood because of difficulties in estimating global biosphere productivity from local reconstructions based on indirect tracers.

To address this, here we use the triple isotopic composition of air oxygen (17Δ = ln(δ17O+1) - λref·ln(δ18O+1), λref = 0.516), which is a biogeochemical tracer of global biosphere primary productivity (Luz et al., 1999). We measured 17Δ of trapped air in the NEEM ice core over 36 to 42 ka interval, covering HS4 and DO8 events. The new NEEM 17Δ data show no significant change over HS4, while CO2 records from multiple ice cores indicate near ~20 ppm increase (e.g., Ahn and Brook, 2014; Bauska et al., 2021). By using the box models describing 17Δ systematics between biosphere-troposphere-stratosphere (e.g., Landais et al., 2007; Blunier et al., 2012), our preliminary results suggest that global biosphere productivity increases during HS4. This result is inconsistent with previous estimates based on ice-core records of non-sea-salt Na and Ca (Fischer et al., 2007), and the marine sediment core opal flux record (Gottschalk et al., 2016), both indicating a reduction of Southern Ocean biological productivity. More 17Δ samples remain to be measured up to the General Assembly 2022 and we hope to have a clearer picture by then.

How to cite: Yang, J.-W., Landais, A., Blunier, T., Duchamp-Alphonse, S., and Prié, F.: Preliminary results of global biosphere productivity reconstruction over Heinrich Stadial 4 from the triple isotopic composition of air oxygen trapped in NEEM ice core, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4287, https://doi.org/10.5194/egusphere-egu22-4287, 2022.

14:30–14:36
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EGU22-9013
Florian Ritterbusch et al.

Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods cannot be readily applied. The noble-gas radioisotopes 81Kr and 39Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. 81Kr (half-life 229 ka) covers the time span of 30-1300 ka, which is particularly relevant for polar ice cores, whereas 39Ar (half-life 268 a) with a dating range of 50-1800 a is suitable for alpine glaciers. For a long time the use of 81Kr and 39Ar for dating of ice samples was impeded by the lack of a detection technique that can measure its extremely small abundance at a reasonable sample size.

We present 81Kr and 39Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for 81Kr and 2-5 kg for 39Ar. Recent studies in Antarctica include 81Kr dating in ice cores from the Larsen Blue ice area, Talos Dome and Epica Dome C. Moreover, we have used 39Ar for dating an ice core from central Tibet covering the past 1500 years, in order to validate a previous timescale based on layer counting. The  studies demonstrate how 81Kr and 39Ar can provide age constraints and complement other methods in developing an ice core chronology. As the sample size requirement for 81Kr and 39Ar analysis still hinders its use in ice cores, developments on the ATTA systems are in progress to further decrease the sample size and increase the dating precision. Here, we present our latest advances towards 81Kr and 39Ar dating with ~ 1 kg of ice.

[1] Z.-T. Lu, et al. (2014) Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214

[2] C. Buizert et al. (2014), Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica Proceedings of the National Academy of Sciences, 111, 6876

[3] L. Tian et al. (2019), 81Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters 46, 6636–6643

[4] Crotti I, et al. (2021) An extension of the TALDICE ice core age scale reaching back to MIS 10.1. Quaternary Science Reviews 266:107078

[5] Lee, G., et al. (2021) Chronostratigraphy of blue ice at the Larsen Glacier in Northern Victoria Land, East Antarctica, The Cryosphere Discuss. [in review]

How to cite: Ritterbusch, F., Crotti, I., Dong, X.-Z., Fourré, E., Gu, J.-Q., Jacob, R., Jiang, W., Landais, A., Lu, Z.-T., Orsi, A., Prié, F., Shao, L., Tian, L., Tong, A.-M., Yang, G.-M., and Wang, J.: Towards 81Kr and 39Ar dating with 1 kg of ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9013, https://doi.org/10.5194/egusphere-egu22-9013, 2022.

14:36–14:42
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EGU22-7641
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ECS
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On-site presentation
Long Nguyen et al.

10Be concentrations measured from ice cores are key records for the reconstruction of long-term changes in solar activity and geomagnetic field intensity. Furthermore, 10Be records have additional applications in the dating of ice cores via the global cosmic ray signal, and studies of snow accumulation rates and atmospheric transport and deposition. Here, we present a new long-term 10Be record from ice chips recovered in austral summer 2017/2018 from Little Dome C, close to Dome Concordia station in East Antarctica and the location of the Beyond-EPICA drilling. The ice chips were drilled by the so-called Rapid Access Isotope Drill method recently developed by the British Antarctic Survey [1]. This new drilling method is based on an auger enclosed in a barrel that quickly collects ice chips instead of recovering a fully intact ice core. The drill design allowed for about 461 m of ice to be drilled in Antarctica in only 104 hours and the chips are suitable for stable water isotope and 10Be analysis. This opens up the prospect of fast recovery of samples for a continuous 10Be record not necessarily connected to a large and costly ice core project.

Our new 10Be record covers the upper 161 meters of ice chips encompassing the last 5000 years. We prepared and measured the ice chip samples using the optimized method demonstrated in our recent publication [2]. We improved the initial timescale of the ice chips via synchronizing changes in the 10Be concentration to changes in the atmospheric 14C concentration inferred from IntCal20. We then reconstruct solar activity and geomagnetic field intensity from the 10Be record using a newly developed Bayesian model aiming at separating the influence of the two processes. The reconstructed solar activity is compared to similar reconstructions based on other ice core 10Be records and the atmospheric 14C record. Similarly, the reconstructed geomagnetic field intensity is compared to the results of global geomagnetic field models that combine paleomagnetic data from archaeological artefacts, igneous rocks and sediments. We highlight the advantages of the new Bayesian model to separate and reconstruct the solar and geomagnetic field signals compared to the conventional methods where an independent geomagnetic field reconstruction is in fact required to reconstruct the solar signal.

 

[1]      J. Rix, R. Mulvaney, J. Hong, D.A.N. Ashurst, Development of the British Antarctic Survey Rapid Access Isotope Drill, J. Glaciol. 65 (2019) 288–298. https://doi.org/10.1017/jog.2019.9.

[2]      L. Nguyen, C.I. Paleari, S. Müller, M. Christl, F. Mekhaldi, P. Gautschi, R. Mulvaney, J. Rix, R. Muscheler, The potential for a continuous 10Be record measured on ice chips from a borehole, Results in Geochemistry. 5 (2021) 100012. https://doi.org/10.1016/j.ringeo.2021.100012.

 

How to cite: Nguyen, L., Nilsson, A., Paleari, C., Müller, S., Christl, M., Mekhaldi, F., Gautschi, P., Mulvaney, R., Rix, J., and Muscheler, R.: A new continuous 10Be record for the last 5000 years measured on ice chips from a borehole in East Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7641, https://doi.org/10.5194/egusphere-egu22-7641, 2022.

14:42–14:48
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EGU22-8140
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ECS
Michael Döring and Markus Christian Leuenberger

Ice core data offers a popular tool to reconstruct high latitude paleo-climate and are often compared to reconstructions from other paleo-archives (e.g. marine sediment cores, pollen records, etc.). For instance, oxygen-stable-isotope (δ18O) of the ice-core water samples is commonly used to reconstruct past site temperatures. However, many high latitude marine temperature reconstructions show low accordance with the spatially inhomogeneous ice core δ18O-based reconstructions over the Holocene on multi-centennial to multi-millennial timescales. For example, many of the δ18O-based Greenland temperature reconstructions do not show a consistent Holocene Thermal Maximum (mid to early Holocene warm period, e.g. for Greenland from 5.4 ± 1.4 ka to 8.6 ± 1.6 ka b2k) found in many high-latitude climate records. The isotopic composition of the water samples provides a rather robust proxy for reconstructing paleo-temperatures for times where large temperature variations occur. In the Holocene where temperature variations are comparatively small, changes in seasonal distribution of precipitation as well as of evaporation conditions at the source region may dominate water-isotope-data variations. In addition, the change of elevation of the Greenland ice sheet over the Holocene leads to an additional temperature signal which is able to mask multi- millennial temperature trends. The use of nitrogen stable isotopes of ancient air trapped in the ice cores provides an alternative for ice core based site temperature reconstructions. This method uses the stability of isotopic compositions of nitrogen in the atmosphere at orbital timescales as well as the fact that changes are only driven by processes in polar firn. Thus gas-isotope-based reconstructions are independent from changes in precipitation seasonality or source signature. Here we present a high-resolution Holocene temperature record from Greenland summit, reconstructed based on nitrogen stable isotopes data (δ15N) from the GISP2 ice core. The reconstruction was conducted by exploiting a Monte Carlo based firn model inversion technique on GISP2 inert gas isotope data, which leads to robust uncertainty estimations. The most robust temperature estimate (T(δ15N)) was compared to a variety of North Atlantic sea surface temperature and terrestrial temperature proxies, showing comparable signatures for multi-centennial to multi-millennial signals. Our record reveals that the warmest period of the Holocene (Holocene Thermal Maximum, HTM) at Greenland summit occurred from 5.4 to 9.2 ka b2k. The HTM was composed by three distinct warm-phases interrupted by several centennial-scale cooling events. We find evidence for a rapid cooling beginning at about 5.4 ka b2k connecting the HTM with the Neoglaciation (long-term cooling trend, 0.4 to 5.1 ka b2k) and for a late Holocene warm-phase 1.3 to 2.2 ka b2k. Furthermore, Greenland warm-phases occurred mostly in times of low solar activity and are synchronous to three Bond-events (ice rafted debris depositions). We find evidence for a coherence of AMOC variability and Greenland summit temperature during the Holocene and conclude therefore that the latter is most likely mainly driven by changes in North Atlantic circulation patterns and AMOC variability for multi-centennial to multi-millennial variability.

How to cite: Döring, M. and Leuenberger, M. C.: Novel Holocene temperature reconstruction of Greenland summit from GISP2 nitrogen isotope data reveals similarities with North Atlantic Circulation and temperature proxies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8140, https://doi.org/10.5194/egusphere-egu22-8140, 2022.