CL1.7

In Austral summer 2017/18 daily surface snow samples were taken (weather allowing) at two depths, 0-1cm and 6-7cm, at Neumayer III Station, Dronning Maud Land DML, Antarctica. Stable isotope ratios (18O, D, d-excess) of the snow samples were analysed in the AWI isotope lab. In parallel, water vapor stable isotopes were measured continuously on a routine base with a Picarro cavity ring-down spectroscope analyser (CRDS). Neumayer III is also a full meteorological observatory measuring all important meteorological variables including upper-air data. Meteorological data were directly compared to both snow and vapor isotope data. The corresponding synoptic situations were analysed using data from AMPS (Antarctic Mesoscale Prediction System), which employs WRF (Weather Research and Forecasting Model), a mesoscale atmospheric model that has been successfully used in earlier studies in DML. AMPS is run operationally at NCAR for Antarctic weather forecasting, particularly for flight operations of the US Antarctic Program (USAP). Additionally, back-trajectory calculations to investigate moisture sources and transport were carried out using FLEXPART, an open-source Lagrangian particle dispersion model. Due to logistical problems, the measuring period during the expedition was too short for statistical analysis, thus we focus on case studies here. In particular, periods with no precipitation were investigated, since earlier studies in Greenland have shown that the interaction of snow surface and atmosphere is important for the stable isotope ratio in the snow, thus in later ice cores that are used to derive paleo temperatures. A better understanding of the highly complex relationship between water vapor stable isotopes and meteorological conditions (including moisture source and transport) as well as the interaction between surface snow and water vapor is necessary for a correct paleoclimatic interpretation of ice cores.

How to cite: Schlosser, E., Bagheri, S., Powers, J. G., Manning, K. W., Hoerhold, M., Behrens, M., and Werner, M.: Atmospheric influences on water stable isotopes in Antarctic water vapor and surface snow – implications for ice core interpretation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2225, https://doi.org/10.5194/egusphere-egu21-2225, 2021.

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 50-1300 ka, which is particularly relevant for polar ice cores, whereas ³⁹Ar (half-life 269 a) with a dating range of 50-1800 a is suitable for high mountain glaciers. For a long time the use of ⁸¹Kr and ³⁹Ar for dating of ice samples was hampered by the lack of a detection technique that can meet its extremely small abundance at a reasonable sample size.

Here, 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 advances in further decreasing the sample size and increasing the dating precision will be discussed. Current studies include ⁸¹Kr dating in shallow ice cores from the Larsen Blue ice area, East Antarctica, in order to retrieve climate signals from the last glacial termination. Moreover, an ³⁹Ar profile from a central Tibetan ice core has been obtained in combination with layer counting based on isotopic and visual stratigraphic signals. The presented studies demonstrate how ⁸¹Kr and ³⁹Ar can constrain the age range of ice cores and complement other methods in developing an ice core chronology.

[1] Z.-T. Lu, Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214, (2014)
[2] C. Buizert, Radiometric ⁸¹Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica, Proceedings of the National Academy of Sciences, 111, 6876, (2014)

[3] L. Tian, ⁸¹Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters, (2019)

http://atta.ustc.edu.cn

How to cite: Ritterbusch, F., Ahn, J., Gu, J.-Q., Jiang, W., Lee, G., Lu, Z.-T., Shao, L., Tian, L., Tong, A.-L., and Yang, G.-M.: Constraining ice core chronologies with 39Ar and 81Kr, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3624, https://doi.org/10.5194/egusphere-egu21-3624, 2021.

Seasonal changes of meteorological and ground surface conditions can cause seasonal changes of source area of mineral particles supplied to the Greenland ice sheet. Difference in metal composition and size distribution of them reflects their source area difference. To clarify seasonal changes in the source area of mineral particles, we examined the metal composition and size distribution of them in snow pit samples obtained from EGRIP (East Greenland Ice Core Project).

In summer 2017, we dug a 2.01 m snow pit at EGRIP camp. Snow samples were collected at 0.03 m intervals. The snow samples were melted, then fractions of them were analyzed for the particle size distribution (0.52-12μm) with a Coulter counter (Beckman Coulter: Multisizer 4). Other fractions of the samples were treated with a microwave acid digestion method to decompose particulates. Total concentrations of Al, Ca and Na in samples were measured by inductively coupled plasma mass spectrometry.

Total concentrations of Al (t-Al) and concentrations of non-sea-salt Ca (nssCa) showed peak values in winter to spring layers. In those layers, nssCa/t-Al ratios and volume fractions of fine particles (<4 μm) tended to be relatively high. In some of those layers, the nssCa/t-Al ratios were 2-3 times higher than the crustal average of Ca/Al ratio. This result suggests that fine Ca-rich mineral particles originated from remote desert areas were supplied to EGRIP in those seasons. In contrast, in summer to autumn layers, the nssCa/t-Al ratios and volume fractions tended to be relatively low. This result can be explained by supplies of coarse (≥ 4 μm) Ca-poor mineral particles originated from soil areas near Greenland in those seasons.

How to cite: Komuro, Y., Nakazawa, F., Goto-Azuma, K., Hirabayashi, M., Shigeyama, W., and Nagatsuka, N.: Recent seasonal changes of metal composition and size distribution of mineral particles in snow at EGRIP, Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4944, https://doi.org/10.5194/egusphere-egu21-4944, 2021.

The aim of the WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial (WACSWAIN) project is to investigate the possible collapse of the West Antarctic Ice Sheet (WAIS) and its surrounding ice shelves during the Last Interglacial (~120,000 years ago).  As part of this project, a 651-meter ice core was drilled to bedrock at Skytrain Ice Rise in Antarctica during the 2018/2019 field season.  Ions and elements originating from marine sources along with water isotope content in this ice core can be used to infer changes in ice sheet and ice shelf extent.  The stable water isotope signal has the potential to capture both regional climate change and changes in the elevation of the drilling site through time.  Marine chemical content in the ice core could indicate variability in the proximity of the site to a marine environment.  Water isotopes and chemical impurities in the ice core were analysed continuously using cavity ring down spectroscopy and inductively coupled plasma mass spectrometry, respectively. As expected, δ¹⁸O and δD increase from the last glacial maximum to the Holocene.  δ¹⁸O and δD increase and sodium and magnesium levels decline from deglaciation into the early Holocene. δ¹⁸O and δD show an abrupt increase in the early Holocene at about 8,000 years before present.  Sea salt similarly increases 2-fold and becomes more variable about 1,000 years later (7,000 years before present).  These increases could indicate a retreat of the ice shelf to its current position.

How to cite: Grieman, M., Hoffmann, H., Humby, J., Mulvaney, R., Nehrbass-Ahles, C., Rowell, I., Thomas, E., and Wolff, E.: WACSWAIN project: isotope and chemical ice core records from Skytrain Ice Rise, Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5504, https://doi.org/10.5194/egusphere-egu21-5504, 2021.

Meteorological regime and glacier surface heat balance, GPR measurements of the ice thickness and seasonal snow cover were investigated in the crater of the Eastern Summit of Mt. Elbrus In the period from 18 to 30 August 2020 at 560 m a.s.l. On the base of preliminary data analysis, the predominance of fluctuations in the synoptic scale over the diurnal ones was revealed; high values of the average and maximum wind speed associated with the influence of jet currents and with the effects of leeward storms were identified; extremely high temporal variability of relative humidity and its very high deficit in cloudless conditions, which contributes to intensive evaporation and sublimation from the snow surface, were explored. The maximum ice thickness in the crater reaches 100 m, with an average of 45 m. A new 96.01 m ice core from glacier surface to bedrock has been recovered. The drilling speed varied from 11 to 1 m / h, decreasing on average with depth from 4.5 to 4.0 m / h. The thickness of the snow-firn strata is about 20 m, which is three times less than on the Western Plateau. The borehole temperature was measured. The temperature on the glacier bedrock was -0.6 °С. The calculated heat flux was 0.39 W/m2. Air sampling was carried out in the crater of the Eastern Summit of Elbrus and on the Garabashi glacier. The repeated measurement of the soil temperature in the fumarole field on the Elbrus Eastern Summit outer crater rim suggests that the temperature regime is stable.

The research was carried out on the territory of the Elbrus National Park with the financial support of the Russian Science Foundation (project 17-17-01270).

How to cite: Kutuzov, S., Mikhalenko, V., Lavrantiev, I., Toropov, P., Vladimirova, D., Abramov, A., and Matskovsky, V.: A new ice core from the Eastern Summit of Mt. Elbrus, Caucasus, Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5973, https://doi.org/10.5194/egusphere-egu21-5973, 2021.

Arctic sea ice has been melting at unprecedented rates in the past decades. Understanding past sea ice variability is of paramount importance to contextualize recent changes and constrain global climate models. Bromine enrichment (Br_enr), relative to sea-water ratio, has been introduced as a proxy of first-year sea ice conditions within the ocean region influencing the ice core location (Spolaor et al., 2013). Br_enr has been measured in ice cores from Greenland, that is the NEEM and RECAP cores. NEEM sea ice proxies are influenced by the region of the Canadian Arctic and Baffin Bay, while for the RECAP core it is mainly the North Atlantic Ocean. In this study we present the first high-resolution record of bromine enrichment from the EGRIP ice core in Greenland for the last 15.7 kyr BP, covering the Holocene-Glacial transition.

From preliminary back-trajectory analyses we suggest that EGRIP sea ice proxy sources are located in a wide region in the Baffin Bay and North Atlantic Ocean. We find EGRIP Br_enr values of ~1 during cold periods, that is the Younger Dryas (12.9 – 11.7 kyr BP) and the last part of the Oldest Dryas (15.7 – 14.7 kyr BP), which we associate with predominant multi-year sea ice conditions. During warmer periods, instead, we observe higher Br_enr values, ~3 for the Bølling-Allerød period (14.7 – 12.9 kyr BP) and progressively higher values from the early Holocene onwards, likely associated with an increased seasonal sea ice area. EGRIP Br_enr is consistent with NEEM and RECAP records and it has the potential to extend our knowledge on Arctic past sea ice variability.

Bibliography

Spolaor, A., Vallelonga, P., Plane, J. M. C., Kehrwald, N., Gabrieli, J., Varin, C., Turetta, C., Cozzi, G., Kumar, R., Boutron, C., and Barbante, C.: Halogen species record Antarctic sea ice extent over glacial–interglacial periods, Atmos. Chem. Phys., 13, 6623–6635, https://doi.org/10.5194/acp-13-6623-2013, 2013.

How to cite: Segato, D., Burgay, F., Maffezzoli, N., Spagnesi, A., Turetta, C., Scoto, F., Dallo, F., Zannoni, D., Erhardt, T., Jensen, C. M., Saiz-Lopez, A., Kjær, H. A., Dahl-Jensen, D., Barbante, C., and Spolaor, A.: A shift to predominant multi-year sea ice conditions in the Baffin Bay and North Atlantic Ocean during the Holocene-Glacial transition inferred from the EGRIP ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6278, https://doi.org/10.5194/egusphere-egu21-6278, 2021.

Dating glaciers is an arduous yet essential task in ice core studies, which becomes even more challenging for the dating of glaciers suffering from mass loss in the accumulation zone as result of climate warming. In this context, we present the dating of a 46 m deep ice core from the Central Italian Alps retrieved in 2016 from the Adamello glacier (Pian di Neve, 3100 m a.s.l.). We will show how the timescale for the core could be obtained by integrating results from the analyses of the radionuclides ²¹⁰Pb and ¹³⁷Cs with annual layer counting derived from pollen and refractory black carbon concentrations. Our results clearly indicate that the surface of the glacier is older than the drilling date of 2016 by about 20 years and that the 46 m ice core reaches back to around 1944. Despite the severe mass loss affecting this glacier even in the accumulation zone, we show that it is possible to obtain a reliable timescale for such a temperate glacier. These results are very encouraging and open new perspectives on the potential of such glaciers as informative palaeoarchives. We thus consider it important to present our dating approach to a broader audience.

How to cite: Jenk, T., Festi, D., Schwikowski, M., Maggi, V., and Oeggl, K.: Dating of ice cores from temperate glaciers - Significant mass loss in the accumulation area of the Adamello glacier indicated by the chronology of a 46 m ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7473, https://doi.org/10.5194/egusphere-egu21-7473, 2021.

The increase in mixing ratio of greenhouse gas (GHG) has been believed to be the primary driver for the ongoing global warming. Among the GHGs, the mixing ratio of nitrous oxide (N₂O) has increased by 23% since 1750 CE. N₂O has a long residence time of ca. 120 years, and a potential to destruct the ozone layer. The Global Warming Potential of N₂O is about 300 times greater than that of CO₂ over 100 years. However, the temporal changes in magnitude and geographic distribution of different N₂O sources are uncertain, hence, understanding the dynamics of atmospheric N₂O has been a challenge to the researcher during the last few decades. Here, we present new stable isotope data of N₂O from the firn air at Styx Glacier, East Antarctica to comprehend the atmospheric evolution for the last 100 years. Our results show that the N₂O mixing ratio has increased, whereas the δ¹⁵N^bulk (‰, AIR) and δ¹⁸O (‰, VSMOW) values decreased during the last 100 years, consistent with the existing firn air records. The progressive increase in the N₂O mixing ratio and the decrease in the isotope ratios suggest a higher contribution from the anthropogenic sources assuming that the N₂O flux from the natural sources is constant. Our box model analysis using the stable isotopes and mixing ratio data of N₂O of Styx firn air suggests that anthropogenic N₂O emission at 2014 CE was ca. 37.5% higher than 1919 CE. The box model calculation with Styx and other firn air and ice core data suggests that in comparison to the pre-industrial era, the total N₂O emission is ca. 61% higher at present (2014 CE), where ca. 62% and 38% contributions are from natural and anthropogenic sources, respectively to the total N₂O emission. The isotope-based mass-balance calculation indicates that continental emission was ca. 45% higher in 2014 CE than in 1919 CE. Although there is a large scatter in existing data, the site preference of ¹⁵N in N₂O molecules (δ¹⁵N^SP ‰, AIR) shows an increasing trend during the post-industrial era, which is consistent with the idea that enhanced fertilization increased soil N₂O emissions by activating nitrification processes.

How to cite: Ghosh, S., Toyoda, S., Ahn, J., Jang, Y., and Yoshida, N.: Understanding the evolution of atmospheric nitrous oxide over the last century from the stable isotopes of the firn air at Styx Glacier, East Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9337, https://doi.org/10.5194/egusphere-egu21-9337, 2021.

Soluble and insoluble impurities play a crucial role regarding the deformability and thus the flow of polar ice. To better understand this interplay from a mechanistic point of view it is especially important to investigate the location and chemical composition of micro-inclusions (Stoll et al., 2021), which are among the most abundant impurities in polar ice.

New results from a systematic analysis of micro-inclusions in Holocene ice from the East Greenland Ice Core Project (EGRIP), which has been drilled near the onset of the Northeast Greenland Ice Stream (NEGIS), offer unique insights into the dynamics of fast flowing ice over different scales, ranging from kilometres to micrometres.

Investigating the small-scale properties of eleven samples from Holocene ice, i.e. the upper 1340 m of the EGRIP ice core, we mapped the locations of several thousand micro-inclusions inside the ice. The use of cryo-Raman spectroscopy allowed us to obtain a representative overview of the mineralogy of these inclusions in the ice without the risk of contamination.

We identified a variety of Raman spectra, mainly from sulphates (dominated by gypsum) and terrestrial dust, such as quartz, mica and feldspar. The observed mineralogy changes with depth and EGRIP Holocene ice can be categorised in two different depth regimes, i.e. the upper (100-900 m) and lower (900-1340 m) regimes, depending on their mineralogy. Furthermore, micro-inclusions show certain spatial patterns, such as clustering or layering, which are partly related to their mineralogy. We thus conclude that Greenlandic Holocene ice has a broader, and more variable, mineralogy than previously reported and that chemical reactions might take place within the ice sheet, possibly altering the paleo-climate record. Our approach further demonstrates the added value of systematic, combined high-resolution impurity and microstructural studies, and the importance of considering different spatial scales and is thus another step towards a more holistic understanding of impurities in ice.

Ref:
Stoll N, Eichler J, Hörhold M, Shigeyama W and Weikusat I (2021) A Review of the Microstructural Location of Impurities in Polar Ice and Their Impacts on Deformation. Front. Earth Sci. 8:615613. doi: 10.3389/feart.2020.615613

How to cite: Stoll, N., Eichler, J., Hörhold, M., Erhardt, T., and Weikusat, I.: Micro-inclusions in the EGRIP ice core identified with Raman-spectroscopy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9900, https://doi.org/10.5194/egusphere-egu21-9900, 2021.

Carbon monoxide (CO) is a regulated pollutant and one of the key components determining the oxidizing capacity of the atmosphere. Obtaining a reliable record of atmospheric CO mixing ratios since pre-industrial times is necessary to evaluate climate-chemistry models in conditions different from today. We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet which experience a range of snow accumulation rates, mean surface temperatures, and different chemical compositions. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled to continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019. The CFA-based CO measurements exhibit excellent external precision (ranging 3.3 - 6.6 ppbv, 1σ), and achieve consistently low blanks (ranging from 4.1±1.2 to 12.6±4.4 ppbv). Good accuracy and absolute calibration of CFA-based CO records enable paleo-atmospheric interpretations. The five CO records all exhibit variability in CO mixing ratios that is too large and rapid to reflect past atmospheric mixing ratio changes. Complementary tests conducted on discrete ice samples demonstrate that such patterns are not related to the analytical process (i.e., production of CO from organics in the ice during melting), but very likely are related to in situ CO production within the ice before analyses. Evaluation of signal resolution and co-investigation of high-resolution records of CO and TOC show that past atmospheric CO concentration can be extracted from the records’ baselines at four sites with accumulation rates higher than 20 cm water equivalent per year (weq yr^-1). However, such baselines should be taken as upper bounds of past atmospheric CO burden. CO records from four sites are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from 1700 to 1957 CE. From 1700 to 1875 CE, this record reveals stable or slightly increasing values remaining in the 100-115 ppbv range. From 1875 to 1957 CE, the record indicates a monotonic increase from 114±4 ppbv to 147±6 ppbv. The ice-core multisite CO record exhibits an excellent overlap with the atmospheric CO record from Greenland firn air which span the 1950-2010 time period. The combined ice-core and firn air CO history, spanning 1700-2010 CE, largely exhibits patterns that are consistent with the recent anthropogenic and biomass burning CO emission inventories. This brand new time series will be compared with the most recent results from Earth System Models involved in the CMIP6-AerChemMIP multi-model exercise.

How to cite: Faïn, X., Rhodes, R., Place, P., Petrenko, V., Fourteau, K., Chellman, N., Crosier, E., McConnell, J., Brook, E., Blunier, T., Legrand, M., Szopa, S., Tsigaridis, K., Naik, V., and Chappellaz, J.: Atmospheric history of carbon monoxide since preindustrial times reconstructed from multiple Greenland ice cores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10171, https://doi.org/10.5194/egusphere-egu21-10171, 2021.

How to cite: Kjær, H. A., Harlan, M., Vallelonga, P., Svensson, A., Blunier, T., Sowers, T., Menking, J. A., de Campo, A., Venkatesh, J., Liisberg, J., Soestmeyer, D., Morris, V., Vaughn, B., and Vinther, B.: Forty years later: High resolution continuous flow analysis of the Dye3 ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11820, https://doi.org/10.5194/egusphere-egu21-11820, 2021.

Ever since the first deep ice cores were drilled, it has been a challenge to determine their original, in-situ orientation. In general, the orientation of an ice core is lost as the drill is free to rotate during transport to the surface. For shallow ice cores, it is usually possible to match the adjacent core breaks, which preserves the orientation of the ice column. However, this method fails for deep ice cores, such as the EastGRIP ice core in Northeast Greenland. We provide a method to reconstruct ice core orientation using visual stratigraphy and borehole geometry. As the EastGRIP ice core is drilled through the Northeast Greenland Ice Stream, we use information about the directional structures to perform a full geographical re-orientation. We compared the core orientation with logging data from core break matching and the pattern of the stereographic projections of the crystals’c-axis orientations. Both comparisons agree very well with the proposed orientation method. The method works well for 441 out of 451 samples from a depth of 1375–2120 m in the EastGRIP ice core. It can also be applied to other ice cores, providing a better foundation for interpreting physical properties and understanding the flow of ice.

How to cite: Westhoff, J., Stoll, N., Franke, S., Weikusat, I., Bons, P., Kerch, J., Jansen, D., Kipfstuhl, S., and Dahl-Jensen, D.: A stratigraphy-based method for reconstructing ice core orientation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13150, https://doi.org/10.5194/egusphere-egu21-13150, 2021.

Since 2018, under the impetus of the IGE (Grenoble) and the LSCE (Saclay) and the common interest of the "Carottes de Glace France" consortium, an analytical platform dedicated to glacier archives was created to meet the growing analytical needs requested by projects involving French partners (Ice Memory, EAIIST, BE-OI ...) and international collaborations with a ten-year vision. Within this framework 5 modules have been developed between the IGE and the LSCE. 3 modules are installed at the IGE, including a CHEMISTRY module which includes a large number of instruments coupled to the CFA (Continuous Flow Analysis) system, allowing high-resolution multi tracer analysis on a single ice stick (water isotopes, dust, conductivity, colorimetry, black carbon, trace metals and gas) as well as several auto-samplers for discrete analyses (major ions, organic species, trace metals, sugars ...). The GAS module is shared between continuous analyses on the CFA system (laser spectrometry CH₄/CO) and discrete analyses (Gas chromatography CH₄/CO₂). The ISOTOPY module allows the analysis of nitrogen (N), sulfur (S) and oxygen (O) isotopes. At the LSCE, the WATER ISOTOPY module allows continuous (Picarro coupled to a CFA line equipped with conductivity cells and auto-sampler) or discrete (Picarro or mass spectrometer) analyses for δD, δ¹⁸O and δ¹⁷O in water. The AIR ISOTOPY module completes the platform for analyses by mass spectrometry of δ¹⁵N of N₂, the triple isotopic composition of O₂ and noble gases isotopes (36/38/40 Ar; 82/84/86 Kr; 129-132 Xe). An overview of the capacity and performance of the platform will be presented.

How to cite: Darfeuil, S., Ginot, P., Savarino, J., Caillon, N., Faïn, X., Teste, G., Landais, A., Fourré, E., Minster, B., and Prié, F.: PANDA, the French analytical platform dedicated to ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13253, https://doi.org/10.5194/egusphere-egu21-13253, 2021.

To recover very old climate information from ice core records, one needs to interpret the deepest part of an ice core. As the oldest record, the Dome-C ice core can serve as an analogue for the Beyond EPICA Oldest Ice Core that is currently being drilled.

Pol et al., EPSL 2010 analyzed high resolution water isotope data from the Dome-C ice core and found evidence for a limited preservation of climate variability in the deep section of the core due to mixing and diffusion. For instance, for Marine Isotope Stage 19, the study estimated a mixing/diffusion length between 40 and 60 cm, a value more than double than what is predicted by current firn and ice diffusion models. Knowing the diffusion length is important to interpret the isotope signal and is the basis to deconvolve climate records. As a result, it is key to bridge the gap in the estimation of the diffusion length between potentially biased statistical methods and firn and ice diffusion models.
We review this diffusion length estimate for MIS19, and also outline a new general method how to estimate the diffusion length in highly thinned deep ice.  This approach presents an important tool for better characterizing the preservation of the climate signal in old ice and thus for designing optimal sampling and recovery strategies.

How to cite: Laepple, T., Münch, T., Kunz, T., Casado, M., and Hoerhold, M.: Estimating the diffusion length in the deepest section of ice cores; A case study for MIS19 in Dome-C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14089, https://doi.org/10.5194/egusphere-egu21-14089, 2021.

With recent advances in analytical techniques, water stable isotope ratios can be measured in astounding detail in ice core records (~mm scale or equivalent to subannual resolution). While this has enabled the study of past climates across a vast range of timescales, the full set of processes driving the highest frequency variability in these water isotope records remains poorly understood. In the EastGRIP ice core, we observe a strong relationship between high-frequency water isotope anomalies (sharp transitions on the scale of cms) and variability in the visual stratigraphy of the ice. The water isotope timeseries reveals these anomalies that would otherwise be missed using traditional lower resolution discrete sampling methods (5-50 cm scale).  A comparison with the dark-field imaging of stratigraphic layers (high-resolution line-scanning system; 50µm/pix) from the EGRIP ice core indicates a correlation between bubble-free ice layers and the sharp transitions observed in the isotope record.  Prior to this comparison, such anomalies in high-resolution isotope records were often dismissed as analytical artifacts. The striking correspondence to the bubble-free ice layers, which is a parameter measured independently from the isotopes, suggests the isotope variability is real. We are investigating a range of depositional and post-depositional processes that may may be able to explain the origin of this variability and its relationship to the physical properties of the ice. This study has implications for frequency analysis of the isotope data, and the related analysis of isotope diffusion and its effects on the recorded climate signal. Understanding these anomalies opens new doors to the interpretation of climate signals in ice cores.

How to cite: Morris, V., Westhoff, J., Vaughn, B., Weikusat, I., Jones, T., Markle, B., Hughes, A., Skorski, W., Brashear, C., Gkinis, V., Vinther, B., and White, J.: Post-depositional processes visible in the integration of EGRIP high-resolution water isotope record and visual stratigraphy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14131, https://doi.org/10.5194/egusphere-egu21-14131, 2021.

In the search for very old ice, finding the age of the ice is a key parameter necessary for its interpretation. Most ice core dating method are based on chronological markers that require the ice to be in stratigraphic order. However, the oldest ice is likely to be found at the bottom of ice sheets, where the stratigraphy is disturbed, or in ablation areas, where the classical methods cannot be used. Absolute dating techniques have recently been developed to provide new constraints on the age of old ice, but their development in the context of ice cores is limited by the large sample size required. Here, we discuss the analytical performances of a new technique for 40Ar dating, which allows us to provide a reliable age with 80g of ice rather than 800g, as previously published. We present an application to the dating of the bottom of the TALDICE and Dome C ice cores. This method represents a significant advance for its application to the very precious ice at the bottom of ice cores.

How to cite: Orsi, A., Crotti, I., Jacob, R., Landais, A., and Fourré, E.: Progress on absolute dating of ice cores with Argon isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14405, https://doi.org/10.5194/egusphere-egu21-14405, 2021.

The Mount Brown South (MBS) ice core is an approximately 300-meter-long ice core, drilled in 2016-2017 to the south of Mount Brown, Wilhelm II Land, East Antarctica. This location in East Antarctica was chosen as it produces an ice core with well-preserved sub-annual records of both chemistry and isotope concentrations, spanning back over 1000 years. MBS is particularly well suited to represent climate variations of the Indian Ocean sector of Antarctica, and to provide information about regional volcanism in the Southern Indian Ocean region.

A section of ice spanning the length of the MBS core was melted as part of the autumn 2019 continuous flow analysis (CFA) campaign at the Physics of Ice, Climate, and Earth (PICE) group at the University of Copenhagen. During this campaign, measurements were conducted for chemistry and impurities contained in the ice, in addition to water isotopes. The data measured in Copenhagen include measurements of H₂O_2, pH, electrolytic conductivity, and NH₄⁺, Ca²⁺, and Na⁺ ions, in addition to insoluble particulate concentrations and size distribution measured using an Abakus laser particle counter.

Here, we present an overview of the CFA chemistry and impurity data, as well as preliminary investigations into the size distribution of insoluble particles and the presence of volcanic material within the ice. These initial chemistry and particulate size distribution data sets are useful in order to identify sections of the MBS core to subject to further analysis to increase our understanding of volcanic activity in the Southern Indian Ocean region.

How to cite: Harlan, M., Kjær, H. A., Vance, T., Vallelonga, P., Gkinis, V., Blunier, T., Svensson, A., Moy, A., Plummer, C., Jackson, S., Peensoo, K., and de Campo, A.: Continuous flow analysis of the Mount Brown South ice core, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15782, https://doi.org/10.5194/egusphere-egu21-15782, 2021.