<figure><img src="image_1.png" /></figure>

<figure><img src="image_2.png" /></figure>

# Ice core dating with the ³⁶Cl/¹⁰Be ratio

Niklas Kappelt<sup>a ID,*</sup>, Raimund Muscheler<sup>a ID</sup>, Mélanie Baroni<sup>b ID</sup>, Juerg Beer<sup>c ID</sup>,
Marcus Christl<sup>d ID</sup>, Christof Vockenhuber<sup>d</sup>, Edouard Bard<sup>b</sup>, ASTER Team<sup>b</sup>, Eric Wolff<sup>e ID</sup>

## ARTICLE INFO

Handling Editor: M. Matthews

Dataset link: https://doi.org/10.5281/zenodo.14209851

### Keywords:

³⁶Cl

¹⁰Be

Radionuclide dating

Ice core

## ABSTRACT

Extremely thinned layers and possible folding make the dating of the deepest sections of ice cores especially challenging. Cosmogenic radionuclides have the potential to provide independent age estimates. The ³⁶Cl/¹⁰Be ratio is largely independent of production rate changes that affect individual radionuclides and has an effective half-life of 384 kyr, making it an ideal tool for dating the new 1.5 Myr old ice core that the Beyond EPICA Oldest Ice Core project aims to retrieve at Little Dome C in East Antarctica. However, the loss of ³⁶Cl through hydrogen chloride outgassing at low accumulation sites complicates its application and the long-term decay of the ³⁶Cl/¹⁰Be ratio in ice has not been studied. Here, we show that ³⁶Cl is preserved in glacial periods and that the ³⁶Cl/¹⁰Be ratio decreases more slowly than expected from physical decay over the last 900 kyr. While the glacial ³⁶Cl flux decreases at the expected rate of physical decay within the uncertainty, the ¹⁰Be flux decreases faster, which may be linked to a post-depositional mobility of ¹⁰Be in deep ice and leads to the slower decrease of the ³⁶Cl/¹⁰Be ratio. In addition to this long-term trend, the ³⁶Cl/¹⁰Be ratio fluctuates around a fitted decay curve, which is likely caused by different climate sensitivities of the transport and deposition pathways of the individual radionuclides. Both effects need to be better understood and quantified to improve age estimates based on the ³⁶Cl/¹⁰Be ratio.

## 1. Introduction

The Beyond EPICA: Oldest Ice Core (BE-OIC) project aims to drill an ice core with an expected bottom age of 1.5 million years at Little Dome C (LDC, 75.30°S, 122.45°E) on the East Antarctic Ice Sheet (Beyond EPICA Consortium, 2023). Determining the age at the bottom of the core will be complicated by extreme layer thinning, as well as possible disturbances of the ice, such as folding (Grootes et al., 1993; Fuchs and Leuenberger, 1996; Chappellaz et al., 1997). Many dating methods rely on assumptions about climate synchronicity and require the correct identification and correlation of signals from different records, such as marine sediment cores. It is therefore desirable to have dating methods, which provide independent age estimates and do not require a continuous stratigraphy.

³⁶Cl is a cosmogenic radionuclide with a half-life of 301 kyr (Endt and van der Leun, 1973), making it a suitable candidate for radioactive decay dating of the oldest ice. It is produced by cosmic ray spallation of ⁴⁰Ar and ³⁶Ar in the atmosphere. The incoming galactic cosmic ray flux and, therefore, the production of ³⁶Cl is modulated by the

magnetic fields of the Sun and the Earth. While this relationship is useful for reconstructions of these fields (Baumgartner et al., 1998; Wagner et al., 2000; Zheng et al., 2021), it introduces a variability in the initial radionuclide concentration and needs to be accounted for when attempting to date any record with the radioactive decay of a single type of cosmogenic radionuclide. Instead of trying to use the ³⁶Cl concentration alone, the ³⁶Cl/¹⁰Be ratio can be utilised, since ¹⁰Be, another radionuclide, is produced in the atmosphere with an almost identical dependency on modulations by the magnetic fields of the Sun and the Earth, resulting in a production rate ratio of 0.0875, largely independent of the cosmic ray flux (Poluianov et al., 2016; Wagner et al., 2000) (see also Figure S1). With a half-life of 1387 kyr for ¹⁰Be (Chmeleff et al., 2010), the effective half-life of the ³⁶Cl/¹⁰Be ratio is 384 kyr. Alternative radionuclide dating methods use the ²⁶Al/¹⁰Be ratio with a combined half-life of 1490 kyr or ⁸¹Kr with a half-life of 229 kyr, but both require a larger sample mass than the ³⁶Cl/¹⁰Be ratio (Auer et al., 2009; Crotti et al., 2021).

<footnote><sup>a</sup> Department of Geology, Lund University, Sölvegatan 12, Lund, 223 62, Sweden</footnote>

<footnote><sup>b</sup> Aix Marseille University, CNRS, IRD, INRAE, Coll. de France, CEREGE, Technopôle de l'Arbois-Méditerranée, Aix-en-Provence, 13545, France</footnote>

<footnote><sup>c</sup> Department of Surface Waters, Swiss Federal Institute of Aquatic Science and Technology, Überlandstraße 133, Dübendorf, 8600, Switzerland</footnote>

<footnote><sup>d</sup> Laboratory of Ion Beam Physics, Swiss Federal Institute of Technology, Otto-Stern Weg 5, Zürich, 8093, Switzerland</footnote>

<footnote><sup>e</sup> Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom</footnote>

<footnote>* Corresponding author.
E-mail address: niklas.kappelt@geol.lu.se (N. Kappelt).</footnote>
Complications for the ³⁶Cl/¹⁰Be ratio arise from the loss of ³⁶Cl at sites with a low snow accumulation rate under present day (interglacial) conditions. Nuclear bomb tests between 1952–1964 constitute a well-defined period with an elevated ³⁶Cl deposition flux 100–1000 times higher than the natural average (Elmore et al., 1982; Heikkilä et al., 2009b). In a snow pit from Vostok in East Antarctica, where the accumulation rate is extremely low at 2.1 g cm⁻² yr⁻¹ (Ekaykin et al., 2002), this bomb peak was found shifted upwards from its expected depth, based on the known age, with elevated ³⁶Cl concentrations still present today, showcasing the mobility of ³⁶Cl, which leads to re-deposition and/or loss (Delmas et al., 2004; Pivot et al., 2019). The mobility has been attributed to gaseous H³⁶Cl, which the authors of Delmas et al. (2004) assume to be the ³⁶Cl-containing compound deposited in the snow at Vostok. At higher accumulation sites, such as Berkner Island and Talos Dome in Antarctica and NGRIP and Dye3 in Greenland this loss of ³⁶Cl is not observed and the bomb peak signal is found at the expected depth (Synal et al., 1990; Pivot et al., 2019; Heikkilä et al., 2009b). The loss of chlorine has been studied in greater detail on bulk chlorine, which originates mainly from sea-salt and can be deposited as sodium chloride (NaCl) or hydrogen chloride (HCl) (Wagnon et al., 1999; Wolff et al., 2010). The latter is created by reactions of sea-salt with nitric acid (HNO₃) and sulfuric acid (H₂SO₄) during transport or after deposition (Legrand and Delmas, 1988; Legrand et al., 2017b). This can be assessed by measuring the Cl⁻/Na⁺ mass ratio, which is 1.80 for freshly emitted sea-salt aerosol (Lyman and Fleming, 1940). Lower values are associated with chlorine loss and can be found in Holocene samples from low accumulation sites such as Vostok (Wagnon et al., 1999) and EPICA Dome C (EDC, accumulation rate 2.7 g cm⁻² yr⁻¹ (Schwander et al., 2001)), where HCl deposition has been found to be reversible (Benassai et al., 2005; Wagnon et al., 1999; Röthlisberger et al., 2003). This can lead to an exchange of sea-salt chlorine with bomb-peak ³⁶Cl and natural ³⁶Cl, emphasising the importance of studying sea-salt concentrations in parallel to radionuclides (Pivot et al., 2019; Delmas et al., 2004). Little Dome C is located only 40 km from EDC, so similar atmospheric conditions can be expected for the new BE-OIC core. The snow accumulation rate is about 8% lower at LDC (Rowell, 2022).

While the loss of ³⁶Cl complicates the dating of ice from low accumulation sites, it may be possible to obtain loss-free samples from glacial periods. In the EDC core, a stable Cl⁻/Na⁺ mass ratio close to the sea-salt reference value of 1.80 suggests that chlorine loss was limited during the Last Glacial Maximum (LGM) (Röthlisberger et al., 2003). This preservation has been attributed to the elevated concentration of alkaline dust, which was about 20 times higher during the LGM compared to the Holocene, as approximated by non-sea-salt calcium (nss-Ca²⁺) (Röthlisberger et al., 2003; Wolff et al., 2010). The dust was estimated to reduce the atmospheric lifetime of HNO₃ by a factor of 25 and affect H₂SO₄ concentrations as well, thereby neutralising the majority of acidic species responsible for the loss of chlorine (Röthlisberger et al., 2002, 2003). Two possible selections of samples have the potential to be unaffected by chlorine loss and therefore be used for age estimates via the ³⁶Cl/¹⁰Be ratio: ice from time periods with high accumulation rates or from periods with high atmospheric dust concentrations. While reconstructions from the EDC core show higher accumulation rates up to 4.6 g cm⁻² yr⁻¹ in interglacial periods of the past (Parrenin et al., 2007), they mostly stay below values of 4–8 g cm⁻² yr⁻¹, which have been suggested as thresholds for chlorine preservation (Röthlisberger et al., 2003; Benassai et al., 2005). In the case of dust, a threshold of 20 µg kg⁻¹ has been suggested for chlorine preservation (Röthlisberger et al., 2003) and large parts of glacial periods exceed this value in the EDC core (Wolff et al., 2010).

The aim of this study is to assess whether ³⁶Cl is preserved under the same conditions that prevent the loss of sea-salt chlorine: high precipitation or high dust concentrations. The Cl⁻/Na⁺ ratio as an indicator for chlorine loss in respect to the sea-salt ratio will be compared to the ³⁶Cl/¹⁰Be ratio as an indicator for ³⁶Cl loss in selected samples from

<table><caption>**Table 1**

Radionuclide samples types.</caption><thead><tr><th></th><th></th></tr></thead><tbody><tr><td><strong>LDC RAID samples</strong></td><td></td></tr><tr><td>LDC drill chips from a rapid access isotope drilling (RAID) campaign (Rowell et al., 2023).</td><td></td></tr><tr><td><strong>EDC ice samples</strong></td><td></td></tr><tr><td>EDC A-cut (approximately quarter core-sections) samples and ice shavings from the outer part of the core, which were created while preparing the inner part for argon measurements (not part of this study).</td><td></td></tr><tr><td><strong>EDC composite samples</strong></td><td></td></tr><tr><td>The ice used for <sup>81</sup>Kr measurements reported in Bouchet et al. Bouchet et al. (2023) was prepared by shaving off about 1 mm of ice from the core before melting the inner part for gas extraction (Florian Ritterbusch, personal communication, 16.01.2023). A composite of <sup>10</sup>Be measurements on the shavings and <sup>36</sup>Cl measurements on the meltwater was used to calculate the <sup>36Cl</sup>/<sup>10</sup>Be ratio for these same samples. Additional <sup>10</sup>Be measurements connected to these samples are discussed in the supplementary information.</td><td></td></tr></tbody></table>

EDC and LDC with a focus on the LGM and the last deglaciation. To assess how the ³⁶Cl/¹⁰Be ratio might perform as a dating method, it was measured in samples of various ages in the EDC core and compared to the expected decay curve.

## 2. Methods

### 2.1. Sample selection

Three types of samples were used for measurements of ¹⁰Be and ³⁶Cl in this study and are presented in Table 1.

The selection and analysis of the samples were carried out with two aims. The first was to test the hypothesis, whether ³⁶Cl is preserved, when either the accumulation rate or dust concentration is sufficiently high and whether the Cl⁻/Na⁺ ratio and ³⁶Cl/¹⁰Be ratio behave the same way in relation to these parameters. For this aim, LDC RAID and EDC ice samples from the last glacial maximum (LGM) to the present were analysed to cover a wide range of values for the Cl⁻/Na⁺ ratio, linked to the different climatic conditions: in the LGM, dust concentrations were high and the Cl⁻/Na⁺ ratio was stable and close to the sea-salt reference value (Röthlisberger et al., 2003), so no loss of ³⁶Cl would be expected. In the early Holocene, the accumulation rate was slightly higher and ³⁶Cl may have been preserved, as the Cl⁻/Na⁺ ratio exceeded the sea-salt reference value at the time, the cause of which will be explored in Section 3.1 as well. For the later Holocene, when both dust concentrations and the accumulation rate were lower, the Cl⁻/Na⁺ ratio is below the sea-salt reference value and loss of ³⁶Cl is expected.

The second aim was to measure the long-term decay of the ³⁶Cl/¹⁰Be ratio in EDC ice and composite samples with ages between 3–887 kyr. Decay corrected samples were analysed for correlations with the Cl⁻/Na⁺ ratio, nss-Ca²⁺ concentrations, deuterium, and the accumulation rate to investigate variations observed in the ³⁶Cl/¹⁰Be ratio. Additionally, the decay of ³⁶Cl and ¹⁰Be was compared separately to the expected decay based on their physical half-lives.

### 2.2. Radionuclide measurements

All ¹⁰Be samples were prepared with 0.299 mg⁹Be carrier and ion exchange columns as described by Adolphi et al. (2014). In most cases, several ¹⁰Be samples were combined into a single ³⁶Cl sample, because ³⁶Cl concentrations in ice are lower than ¹⁰Be concentrations, and a larger sample volume is required for a measurement. The ³⁶Cl/¹⁰Be ratio was calculated with the average of the corresponding ¹⁰Be concentrations weighted by their sample weight and uncertainties for the ³⁶Cl/¹⁰Be ratio were calculated with Gaussian error propagation. All ³⁶Cl samples were prepared following the procedure described by Delmas et al. (2004) with the addition of 4.0 mg of stable chlorine
carrier to most samples. A table specifying all sample weights, Cl carrier amounts, radionuclide concentrations and uncertainties can be found in Table S1 in the supplementary information.

After sample preparation, the ¹⁰Be content was determined with Accelerator Mass Spectrometry (AMS), either at the ASTER facility at CEREGE or at the Laboratory for Ion Beam Physics at ETH Zurich. ¹⁰Be/⁹Be ratios were normalised to the ASTER in-house standard STD-11 with a nominal ratio of ¹⁰Be/⁹Be = (11.91 ± 0.13) · 10⁻¹² at CEREGE (Braucher et al., 2015) and to the ETH in-house standard S2007N with a nominal ratio of ¹⁰Be/⁹Be = (28.1 ± 0.8) · 10⁻¹², which in turn is normalised against the ICN 01-5-1 standard with a nominal value of ¹⁰Be/⁹Be = 2.709 · 10⁻¹¹ (Nishiizumi et al., 2007), at ETH Zurich (Christl et al., 2013). All ³⁶Cl samples were measured at ETH Zurich and normalised with the in-house standard K382/4N (Christl et al., 2013), which has a nominal value of ³⁶Cl/Cl = (17.36 ± 0.34) · 10⁻¹². The average blank and sample ¹⁰Be/⁹Be ratios measured at CEREGE were (3.01 ± 0.96) · 10⁻¹⁴ and (1.10 ± 0.58) · 10⁻¹², respectively. At ETH Zurich, the average blank and sample ¹⁰Be/⁹Be ratios were (3.11 ± 1.45) · 10⁻¹⁴ and (2.62 ± 1.39) · 10⁻¹², respectively and the average blank and sample ³⁶Cl/³⁵Cl ratios were (3.72 ± 2.03) · 10⁻¹⁵ and (9.44 ± 0.64) · 10⁻¹⁴. All ¹⁰Be and ³⁶Cl samples were blank corrected with the blanks prepared in parallel to the respective samples.

Eleven EDC A-cut samples with ages between 2.8 and 128 kyr were split into two aliquots after homogenisation and ¹⁰Be was measured at CEREGE and at ETH Zurich for an inter-lab comparison. The results correlate with r = 0.999 and are plotted against each other in Figure S2 in the supplementary information. The ¹⁰Be content of EDC ⁸¹Kr sample shavings and all LDC samples was determined at ETH Zurich and the ¹⁰Be content of all other EDC ice samples at CEREGE. For the composite EDC samples, ³⁶Cl concentrations were measured in separate samples of the same ⁸¹Kr meltwater at both CEREGE and ETH Zurich. Reported values are average of both measurements, see Figure S3 in the supplementary information for an overview and a discussion of all radionuclide measurements on EDC ⁸¹Kr samples. All other ³⁶Cl concentrations were determined at ETH Zurich.

## 2.3. Correction with theoretical production rates

As part of the analysis of individual radionuclides, the ³⁶Cl and ¹⁰Be fluxes were adjusted with geomagnetic field based estimates for the production rate. The fluxes were normalised to their respective mean values and divided by calculated production rates, normalised to their respective mean values. The production rates were calculated according to Poluianov et al. (2016) using the local interstellar spectrum published by Herbst et al. (2017), the yield functions published by Poluianov et al. (2016), the geomagnetic field reconstruction of Channell et al. (2009) (PISO-1500 stack) and a solar modulation parameter of $\Phi = 550$ MV. There is no reconstruction of the solar modulation before the Holocene, so $\Phi$ was kept constant. The chosen value has no influence on the results, as the calculated production rates were normalised by division through their mean. The possible influence of variable solar modulation is part of the discussion. To synchronise the age scales of the geomagnetic field data and the EDC radionuclide data, the $\delta^{18}$O peaks of the PISO-1500 stack were matched to the peaks of the EDC deuterium record (Jouzel et al., 2007; Veres et al., 2013) with linear interpolation of the age scale in between peaks. Because EDC deuterium and benthic $\delta^{18}$O do not necessarily change completely synchronously, an uncertainty of up to a few thousand years may remain. The matched records are shown in Figure S7 in the supplementary information.

# 3. Results and discussion

## 3.1. LGM and last deglaciation

Fig. 1 shows decay corrected ³⁶Cl/¹⁰Be ratio data from LDC over the last deglaciation together with deuterium and Cl⁻/Na⁺ ratio data

from Rowell et al. (2023). Also included are decay corrected ³⁶Cl/¹⁰Be ratio data from EDC together with Cl⁻/Na⁺ ratio data from Wolff et al. (2010).

As expected from previous studies (Delmas et al., 2004; Pivot et al., 2019), the ³⁶Cl/¹⁰Be ratio indicates the loss of ³⁶Cl in the Holocene. The theoretical production rate ratio of 0.0875 is shown as a dashed black line and observed values are significantly lower. This is similar to the loss of Cl⁻ at EDC and LDC in the Holocene, which has been described in several studies (Benassai et al., 2005; Röthlisberger et al., 2003) and is evident in the Cl⁻/Na⁺ ratio, which falls below the sea-salt value of 1.80 (dashed line) (Röthlisberger et al., 2003; Rowell et al., 2023; Lyman and Fleming, 1940). The similarity is even found for the above average ³⁶Cl/¹⁰Be ratio around 7kyr BP in the EDC core, as the Cl⁻/Na⁺ ratio is elevated above the Holocene average to 0.93 as well (see also Figure S4), although there is no obvious cause for the increase in both ratios.

In the early Holocene (around 12 kyr BP), not only does the ³⁶Cl/¹⁰Be ratio at LDC indicate the preservation of ³⁶Cl, but the Cl⁻/Na⁺ ratio at EDC suggests an excess of Cl⁻ compared to the sea-salt reference. One possible cause for an elevated Cl⁻/Na⁺ ratio is the depletion of sodium through the precipitation of mirabilite (Na₂SO₄) on newly forming sea-ice. However, this process is linked to the increased formation of sea-ice in glacial times and can only cause a maximum Cl⁻/Na⁺ ratio of 2.2, because it is limited by the sulphate content in sea-water (Rankin et al., 2004), so it cannot be responsible for the high values observed at the beginning of the Holocene. Instead, higher accumulation has been found to preserve HCl gas, which is generated in reactions between sea-salt and acidic species, and becomes an important source of chloride only at remote sites, like LDC and EDC, where the sea-salt flux is low (Benassai et al., 2005; Legrand et al., 2017b; Legrand and Delmas, 1988). While the deposition is reversible under present day conditions, it has been suggested that higher accumulation rates can preserve the additional chloride (Röthlisberger et al., 2003; Wagnon et al., 1999), even though they only reach 3.2 g cm⁻² yr⁻¹ at EDC and approximately 2.9 g cm⁻² yr⁻¹ at LDC (92% of the EDC value as estimated by Rowell in the early Holocene (Rowell, 2022)) (Wolff et al., 2010), thereby remaining below the 4–8 g cm⁻² yr⁻¹ water equivalent of precipitation that has been suggested as the threshold for preservation (Benassai et al., 2005; Röthlisberger et al., 2003).

During the last glacial maximum, higher concentrations of alkaline dust neutralised acidic species and thereby prevented the conversion of sea-salt chloride to hydrogen chloride gas (Röthlisberger et al., 2003). The result is a stable Cl⁻/Na⁺ ratio close to the sea-salt value of 1.80 in samples older than 17 kyr BP in Fig. 1. The glacial ³⁶Cl/¹⁰Be ratio data from LDC and EDC (lowest two and three values, respectively) suggest the same preservation for ³⁶Cl with average decay corrected ³⁶Cl/¹⁰Be ratios of 0.0917 and 0.120, respectively, higher than the production rate ratio of 0.0875 in both cases. The average decay corrected ³⁶Cl/¹⁰Be ratio from a series of measurements around 7400 yr BP (interglacial) from Dome Fuji is similarly high with a value of 0.123 (Kanzawa et al., 2021). In Greenland, even higher values can be found in the ice cores drilled at GRIP (0.20 in the Holocene, 0.27 in the last glacial), Dye3 (0.16, Holocene), and Milcent (0.18, Holocene) (Yiou et al., 1997; Baumgartner et al., 1997a; Muscheler et al., 2004; Wagner et al., 2001; Muscheler, 2000; Lukasczyk, 1994). Since the production rate ratio can hardly be changed, the shift towards higher values must occur during the transport or the deposition of the radionuclides. ¹⁰Be in air masses may be washed out by precipitation while moving from mid-latitudes towards the poles, as shown by Pedro et al. (2011). A washout of ³⁶Cl is likely as well, but the removal efficiency may differ between the two radionuclides, especially if ³⁶Cl is transported as a gas. A recent modelling study (M. Zheng, manuscript submitted) supports the hypothesis that ³⁶Cl predominantly exists in the gas phase. Zheng et al. analysed ³⁶Cl deposition fluxes with the ECHAM6.3-HAM2.3 model in two configurations: one assuming that ³⁶Cl is attached to aerosols, similar to the behaviour of ¹⁰Be, and another assuming that
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Decay corrected $^{36}$Cl/$^{10}$Be ratio in LDC and EDC samples from the LGM to the present. At Little Dome C, the $^{36}$Cl/$^{10}$Be ratio follows the pattern of the Cl$^-$/Na$^+$ ratio, which is mainly determined by chloride loss. The dashed black lines show the calculated production rate ratio of $^{36}$Cl/$^{10}$Be, 0.0875, in the $^{36}$Cl/$^{10}$Be panel, the sea-salt reference value of the Cl$^-$/Na$^+$ ratio, 1.80, in the Cl$^-$/Na$^+$ panels and the nss-Ca$^{2+}$ threshold for chlorine preservation, 20 µg kg$^{-1}$, as suggested by Röthlisberger et al. in the nss-Ca$^{2+}$ panel. The yellow shaded area marks the Antarctic Cold Reversal (ACR). LDC deuterium and ion data are published in Rowell et al. (2023) and EDC ion data is published in Wolff et al. (2010).</figcaption></figure>

$^{36}$Cl is primarily in the gas phase. In the aerosol-attached configuration, the $^{36}$Cl/$^{10}$Be ratio remained constant across latitudes, while the gas-phase configuration resulted in an increasing $^{36}$Cl/$^{10}$Be ratio towards the poles, which aligns more closely with observations. Instead of a washout effect, however, Zheng et al. explain this with a higher scavenging efficiency of HCl gas compared to aerosols in mixed phase (liquid and ice) clouds. This would mean, that increased $^{36}$Cl/$^{10}$Be ratios would be more pronounced at sites with wet deposition, rather than dry deposition, which would explain the overall higher values in Greenland compared to Antarctica. It would also offer an explanation for higher $^{36}$Cl/$^{10}$Be ratios at EDC than at LDC, since the accumulation rate is slightly higher at EDC.

During the Antarctic cold reversal (ACR, ca. 14.5–12.5 kyr BP), both, Cl⁻ and $^{36}$Cl are depleted with respect to Na⁺ and $^{10}$Be, respectively. Similar to the present day, this is likely due to neither the accumulation rate nor the dust concentration being sufficiently high to preserve sea-salt chloride or $^{36}$Cl.

Overall, the decay corrected $^{36}$Cl/$^{10}$Be ratio appears to follow the same behaviour as the Cl$^-$/Na$^+$ ratio, which suggests that the latter can be used as an indicator for $^{36}$Cl-loss-free samples. For LDC, the decay corrected $^{36}$Cl/$^{10}$Be ratio and the Cl$^-$/Na$^+$ ratio correlate with $r = 0.97$ ($p < 0.01$), but only five samples with overlapping ion and radionuclide data are available, so this correlation should be treated with caution. For EDC, the two ratios correlate with $r = 0.95$ ($p < 0.005$, n = 7, see Figure S4). In both cores, the linear relationships indicate that the $^{36}$Cl/$^{10}$Be production rate ratio of 0.0875 is already reached at Cl$^-$/Na$^+$ ratios below the sea-salt reference value of 1.8 (1.6 at LDC and 1.2 at EDC), suggesting that $^{36}$Cl is preserved more easily than Cl⁻. Overall, these results support the hypothesis that glacial samples can be used for dating ice with the $^{36}$Cl/$^{10}$Be ratio.

## 3.2. Long-term decay

The measured $^{36}$Cl/$^{10}$Be ratio from various depths in the EDC core is shown in Fig. 2 together with the accumulation rate (Bouchet et al.,
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** $^{36}$Cl/$^{10}$Be ratio in the EDC core. The accumulation data, which is published in Bouchet et al. (2023), demonstrates that most samples are from glacial periods. The ion data are published in Wolff et al. (2010) and help to determine which samples might be affected by $^{36}$Cl loss with either a Cl$^-$/Na$^+$ ratio below the sea-salt reference value of 1.80 (dashed line) or a nss-Ca$^{2+}$ concentration below 20 µg kg$^{-1}$ (dashed line).</figcaption></figure>

2023), the Cl$^-$/Na$^+$ ratio and the nss-Ca$^{2+}$ concentration (Wolff et al., 2010). Different marker symbols are used to distinguish between the two types of EDC samples and to mark the accumulation and ion data at the corresponding depths of the radionuclide samples.

The $^{36}$Cl/$^{10}$Be ratio does not steadily decrease with depth, but most data points that deviate from a smooth decay trend do so consistent with expectations: a major influence is the loss of $^{36}$Cl. While most samples originate from glacial periods and are expected to be only mildly or not affected by $^{36}$Cl loss, some samples were specifically selected from warmer periods with a Cl$^-$/Na$^+$ ratio far below the sea-salt reference value and a low nss-Ca$^{2+}$ concentration, as discussed in the previous section. Samples which are very likely to have suffered from $^{36}$Cl loss are all Holocene samples, the two samples with an age around 90 kyr BP and the sample with an age of 470 kyr BP, which stands in contrast to the slightly younger sample from a colder period without $^{36}$Cl loss.

<table><caption>**Table 2**
Correlations between the decay corrected $^{36}$Cl/$^{10}$Be ratio and other data in the EDC core.</caption><thead><tr><th>Variable</th><th>r</th><th>p</th></tr></thead><tbody><tr><td>Cl<sup>-</sup>/Na<sup>+</sup></td><td>0.57</td><td>0.0038</td></tr><tr><td>Cl<sup>-</sup>/Na<sup>+</sup> &lt; 1.80</td><td>0.68</td><td>0.00066</td></tr><tr><td>nss-Ca<sup>2+</sup></td><td>0.57</td><td>0.0071</td></tr><tr><td>Accumulation rate</td><td>-0.16</td><td>0.47</td></tr><tr><td>Deuterium</td><td>-0.23</td><td>0.27</td></tr><tr><td>Age</td><td>0.40</td><td>0.046</td></tr><tr><td>Depth</td><td>0.40</td><td>0.047</td></tr></tbody></table>

Potentially affected are the samples around 600 kyr BP, but, due to the spread in the data, they do not stand out with values which are obviously too low. When compared over the entire EDC dataset, the
Cl⁻/Na⁺ ratio and the decay corrected ³⁶Cl/¹⁰Be ratio correlate with r = 0.57 (p < 0.005), weaker than in the LDC and EDC datasets of only the last 30,000 years. The r and p values of different correlations that were tested are listed in Table 2, scatter plots can be found in Figure S5 in the supplementary information. When only considering data points with a Cl⁻/Na⁺ ratio below 1.80, the correlation becomes stronger with r = 0.68 (p < 0.001), which is expected, as values for the Cl⁻/Na⁺ ratio below the sea-salt reference value of 1.80 signify a loss of Cl⁻ and indicate a loss for ³⁶Cl, while higher values mean an excess of Cl⁻ in respect to Na⁺, which does not necessarily imply an excess of ³⁶Cl in respect to ¹⁰Be, since they come from different sources and are transported differently. Nonetheless, the ³⁶Cl/¹⁰Be ratio is elevated concurrent to the peak of the Cl⁻/Na⁺ ratio during the Eemian, hinting towards a common mechanism for enhancement. However, the relationship between the two ratios in this domain cannot be described with the linear correlation of samples with a Cl⁻/Na⁺ ratio below 1.8, which is only valid for the dependency related to HCl loss. The high accumulation rate during the Eemian may have preserved ³⁶Cl in the EDC core, which was mobilised as H³⁶Cl under acidic atmospheric conditions elsewhere on the Antarctic ice sheet, similar to the mechanism that temporarily enables Cl⁻/Na⁺ ratios above the sea-salt reference value (Benassai et al., 2005). Alternatively, increased washout of ¹⁰Be or increased wet deposition from mixed phase clouds in a period of high precipitation may cause an increase in the ³⁶Cl/¹⁰Be ratio. This supports the hypothesis that samples from glacial periods are best suited for dating ice cores from low accumulation sites with the ³⁶Cl/¹⁰Be ratio, since higher concentrations of alkaline dust neutralise acidic species, which otherwise disturb the chloride and ³⁶Cl signal, even when high accumulation rates limit the loss at the drilling location. Dust concentrations can be approximated with the nss-Ca²⁺ concentration and a threshold of 20 µg kg⁻¹ has been suggested for Cl⁻ preservation (Röthlisberger et al., 2003). As noted in the discussion of Fig. 1, however, a comparison of the two ratios suggests preservation of ³⁶Cl with a lower threshold. The decay corrected ³⁶Cl/¹⁰Be ratio correlates with the nss-Ca²⁺ concentration in the EDC core with r = 0.57 (p < 0.01) and ³⁶Cl/¹⁰Be ratios around the production rate ratio of 0.0875 are reached for samples with a nss-Ca²⁺ concentration above 10 µg kg⁻¹ (see Figure S5). While aeolian dust may also add resuspended ¹⁰Be to the ice (Lal, 2007), the mean contribution to the presented ¹⁰Be samples is low with an average of 2.4 ± 2.4%, calculated with a ¹⁰Be concentration of 6.5 · 10⁹ atoms per gram of dust, as suggested by Lal, and the EDC dust record (EPICA Community Members, 2004; Lal, 2007).

Neither correlation is strong enough to warrant corrections of the ³⁶Cl/¹⁰Be ratio based on the Cl⁻/Na⁺ ratio or nss-Ca²⁺ concentration, but it justifies limiting the sample selection to glacial samples, before fitting a decay curve to the data. In Fig. 3, such a fit using only glacial ³⁶Cl/¹⁰Be data is presented in black with a shaded green area indicating the one σ uncertainty of the decay constant and the intercept.

Even with the limitation to glacial samples, which are presumably unaffected by chlorine loss, variations in the ³⁶Cl/¹⁰Be ratio can be observed, which results in deviations from the fitted curve. They could be caused by differences in the transport and deposition of the two individual radionuclides, which are linked to their different chemical properties: ¹⁰Be quickly attaches to sulphate aerosols (Heikkilä et al., 2013) and ³⁶Cl can attach to aerosols or form H³⁶Cl gas (Zerle et al., 1997; Heikkilä et al., 2009b). Due to its relevance for geomagnetic field and solar activity reconstructions (e.g. Muscheler et al., 2005; Zheng et al., 2021; Nguyen et al., 2022), several studies have focused on the production, transport and deposition of ¹⁰Be. The majority (65%) is produced in the stratosphere (Heikkilä and Smith, 2013), where its residence time is 1–2 years and the signal becomes hemispherically well mixed, which is why ¹⁰Be records are generally assumed to reflect the global or at least the hemispherical production (Heikkilä and Smith, 2013; Raisbeck et al., 1981; Heikkilä et al., 2009a; Nilsson et al., 2024). Globally, the deposition flux of ¹⁰Be is governed by the

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** ³⁶Cl/¹⁰Be ratio in the EDC core with a fitted decay curve as a solid black line with a shaded green area demonstrating the one σ uncertainty of the decay constant and the intercept. The dashed red curve shows the expected decay with an effective half-life of 384 kyr and the decay corrected LGM ³⁶Cl/¹⁰Be ratio of 0.120 as the intercept. Data from interglacial periods were excluded from the fit and are shown in grey.</figcaption></figure>

stratosphere–troposphere exchange at mid-latitudes and precipitation, as wet deposition is much more effective than dry deposition (Heikkilä et al., 2009a). In the Antarctic desert, however, dry deposition accounts for up to 60% of the total ¹⁰Be deposition (Raisbeck and Yiou, 1985; Heikkilä and Smith, 2013) and about one third of the deposited ¹⁰Be originates from the troposphere (Heikkilä et al., 2009a). Additionally, direct descent of stratospheric air over the Antarctic plateau can be a source of deposited ¹⁰Be (Raisbeck et al., 1981; Baroni et al., 2019; Legrand et al., 2017a), especially in summer–autumn, when the tropopause height is at its minimum (Pedro et al., 2011).

For ³⁶Cl, wet and dry deposition fractions have not been determined and the atmospheric transport is usually assumed to be similar to that of ¹⁰Be, even though ³⁶Cl can be found as H³⁶Cl gas. In records from both Antarctica and Greenland, the ³⁶Cl/¹⁰Be ratio variability is similar to the one reported for EDC and LDC here. As discussed before, different degrees of washout during transport and a higher H³⁶Cl scavenging efficiency in mixed-phase clouds may cause these variations. In this case, wet deposition would contribute to higher ³⁶Cl/¹⁰Be ratios, while the influence of dry deposition onto the ice sheets is more uncertain. It mainly depends on the particle size for diffusion and gravitational settling of ¹⁰Be and on the temperature for H³⁶Cl gas adsorption (Diehl et al., 1995; Thibert and Dominé, 1998). Additionally, more mixed-phase than liquid clouds would be expected at lower temperatures, leading to higher ³⁶Cl/¹⁰Be ratios in colder periods. As shown in Table 2, no correlation with the deuterium record exists, but if the exceptionally high δD values from the Eemian are ignored, the data hint towards the proposed negative correlation.

Besides the spread in the ³⁶Cl/¹⁰Be ratio data, the signal is expected to decrease with the effective half-life of 384 kyr, which is shown with the dashed red decay curve in Fig. 3. A decay curve fitted to the data yields an apparent half-life of 457 ± 81 kyr, which is in agreement with the physical half-life within uncertainty, but close to an overestimation. This is also reflected in a positive correlation between the decay corrected ³⁶Cl/¹⁰Be ratio and the age of the ice with r = 0.40 (p < 0.05). This apparently slow decline over time may be caused by a post-depositional effect in deep ice, which will be discussed in the next section.

### 3.3. Individual radionuclides

While the ³⁶Cl/¹⁰Be ratio theoretically removes changes in the radionuclide production rates, its values can be sensitive to processes
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Fluxes of ³⁶Cl and ¹⁰Be in the EDC core. An exponential decay curve was fitted to each radionuclide data set with shaded areas representing the one σ uncertainty range of both, the decay constant and the intercept. Only glacial data were used for the fit to ³⁶Cl fluxes. Decay curves with the respective physical half-life are shown with intercepts identical to those of the fits as dashed red curves.</figcaption></figure>

unrelated to production, as discussed above. Here, we analyse the two radionuclides individually to investigate transport and deposition changes as well as potential post-depositional effects. Their deposition is mostly dry at EDC (Heikkilä et al., 2013; Raisbeck and Yiou, 1985) and their concentrations are influenced by dilution effects from precipitation. Therefore, the fluxes of ³⁶Cl and ¹⁰Be were considered more representative of the production signal and calculated with the accumulation data from Bouchet et al. Bouchet et al. (2023). No flux could be calculated for the lowermost sample, since there is no associated accumulation data. The fluxes are presented in Fig. 4.

The accumulation rate and the decay corrected ³⁶Cl concentration correlate with $r = -0.60$ ($p < 0.005$), while no correlation exists with the decay corrected flux, suggesting that the deposition is, indeed, predominantly dry. An exponential decay fit to the ³⁶Cl flux from glacial periods yields a half-life of 274 ± 27 kyr, which is shown with a solid black line and a shaded green area representing the one σ uncertainty calculated from the uncertainties of the decay constant and the intercept. The expected decay with the physical ³⁶Cl half-life of 301 kyr and the same intercept as the fit is shown as a dashed red line. Even though the fitted decay curve resembles the expectation well and the half-life agrees with the physical value within the uncertainty, it is important to remember that, contrary to the ³⁶Cl/¹⁰Be ratio, all values are affected by production rate variations. A correction of the flux with the geomagnetic field reconstruction of Channell et al. however, barely changes the distribution presented in Fig. 4 and yields a half-life of 298 ± 39 kyr, in slightly better agreement with the physical half-life. The effect of solar modulation can only be estimated, since no reconstruction extends beyond the Holocene, but no long-term effect is expected. Over the last 9400 years, the reconstruction of Nilsson et al. suggests a standard deviation from the mean production rate of 9.7%, when using the current geomagnetic field strength of 7.8 · 10²² A m² and 44-year averages, which corresponds to the radionuclide sample resolution in the LGM (Nilsson et al., 2024). The maximum deviation from the mean production rate in this period are minus 19% and plus 34%. For older samples the possible influence would be smaller,

because their time resolution is lower. However, a weak solar magnetic field could have, for example, caused high production rates around 550 kyr BP and be responsible for the slightly higher ³⁶Cl flux around that time.

If all ³⁶Cl data were to be included in the fit, the apparent half-life would increase to 327 ± 52 kyr or 323 ± 38 kyr, if using the production corrected data, but the complicated interpretation of interglacial chlorine data justifies focusing solely on the glacial flux.

As described in the previous section, changes in the atmospheric transport and deposition of ¹⁰Be can influence its deposition flux on various timescales, which is why production signal reconstructions are more reliable with stacks of ¹⁰Be data from different drilling sites, while individual records can show a certain scatter and biases (Muscheler et al., 2016). The standard deviation of the decay corrected ¹⁰Be flux from the mean is 24%, similar to the 25% observed for the glacial ³⁶Cl flux. In strong contrast to the ³⁶Cl data, however, the decay curve fitted to the ¹⁰Be flux yields a half-life of 618 ± 78 kyr, about 65% lower than the actual half-life of 1387 kyr. Additionally, low ¹⁰Be fluxes around 650 and 750 kyr BP appear to drive the ³⁶Cl/¹⁰Be ratio up above the fitted curve in Fig. 3. Changes in the production signal provide a partial explanation for this: a correction with calculated production data based on the magnetic field reconstruction by Channell et al. leads to a fit with an apparent half-life of 835 ± 150 kyr, closer to the expectation (see Figure S8). One might also challenge the assumption of dry deposition in this context, since a fit to the ¹⁰Be concentration yields a half-life of 961 ± 230 kyr or 1194 ± 396 kyr if using production corrected data. Both, the decay corrected ¹⁰Be concentration and flux correlate with the accumulation rate ($r = -0.55$ ($p < 0.0005$) and $r = 0.51$ ($p < 0.001$), respectively), so neither of them seem to reflect only the production signal.

Another potential cause for the short, apparent half-life of the fit to the ¹⁰Be flux is a possible post-depositional effect, which can influence the ¹⁰Be concentration in deep ice. The radionuclide has been shown to associate with dust in the deepest 100 m of the GRIP core in Greenland Baumgartner et al. (1997b), which can lead to a
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** The relative age uncertainty for dating EDC ice with the $^{36}$Cl/$^{10}$Be ratio, based on the current measurement and half-life uncertainties of $^{36}$Cl and $^{10}$Be. The curves depict an idealised scenario in which radionuclide concentrations are only determined by radioactive decay with present day values reflecting the average, decay-corrected radionuclide concentrations in the EDC ice core.</figcaption></figure>

local depletion or enhancement. Likely connected to this effect are the $^{10}$Be concentration spikes reported for the deepest part of the EDC core with sample ages of 700–800 kyr BP (Raisbeck et al., 2006). Raisbeck et al. suspected that the migration occurs predominantly in horizontal direction, because smoothing over several thousands of years does not yield a distribution resembling the expected production signal smoothed by a vertical migration. In an alternative approach, Auer et al. investigated the $^{26}$Al/$^{10}$Be ratio, which has the advantage that $^{26}$Al and $^{10}$Be behave chemically similarly: both attach to aerosols and should not suffer from the differences in transport and deposition which are a likely cause for the scatter in the $^{36}$Cl/$^{10}$Be ratio. In the deep, undated part of the EDML ice core, however, large variations of the $^{26}$Al/$^{10}$Be ratio were measured and could only be explained by a mobilisation of impurities, which acts differently on the two radionuclides (Auer et al., 2009). While Raisbeck et al. measured $^{10}$Be peaks in 11 cm long samples weighing only 50 g, Auer et al. measured a peak in the $^{10}$Be/$^{26}$Al ratio in several kilograms of ice, approximately spanning over an entire meter of depth. With the discontinuous samples measured in the EDC core, which cover 55 cm of depth in the case of an ice sample and several meters in the case of combined samples, it is difficult to judge whether $^{10}$Be is depleted due to migration in the oldest samples, but the process would offer an explanation as to why the concentration decreases faster with depth than one would expect solely based on radioactive decay. No peaks in the $^{10}$Be concentration or flux were encountered, but with only three samples older than 700 kyr BP this should not be unlikely considering the small number of spikes encountered by Raisbeck et al. in continuous 11 cm samples over about 100 m (see also comparison in Figure S9).

### 3.4. Potential for absolute age estimates

Fig. 5 shows the relative uncertainty for age estimates with the $^{36}$Cl/$^{10}$Be ratio using different masses of ice. For the calculation, constant values for the $^{36}$Cl and $^{10}$Be concentrations at the time of their deposition are assumed. For a sample of a given mass and age, the number of atoms would be known and determine the measurement uncertainty (see Figure S10 and S11). Together with the uncertainty of the $^{36}$Cl and $^{10}$Be half-lives, an idealised dating uncertainty can be estimated. In regards to the expected age of 1.5 Myr for the newly drilled Beyond EPICA Oldest Ice Core, the $^{36}$Cl/$^{10}$Be ratio has the potential to provide age estimates with lower uncertainties and using less sample mass than the $^{26}$Al/$^{10}$Be ratio, which has estimated measurement uncertainties of 30–40% for 7–14 kg of ice (Auer et al., 2009). Approximately half as much ice would be needed at EDC or

LDC, where the $^{10}$Be concentrations are about twice as high as in ice from EDML (Ruth et al., 2007), which the calculation by Auer et al. is based on. The $^{81}$Kr measurements performed on the samples whose shavings and meltwater have been used for the composite EDC samples in this study provided three age estimates with about 10% uncertainty using 6.0 to 8.4 kg of ice (Bouchet et al., 2023). Remarkably, about half of the uncertainty originates from the uncertainty of the $^{81}$Kr half-life and improvements of the measurement procedure aim to reduce the required sample mass to just 1.0 kg (Florian Ritterbusch, personal communication). The downside of $^{81}$Kr dating is the shorter $^{81}$Kr half-life of $t_{1/2} = 227$ kyr (Baglin, 2008), which leads to a faster increase of the relative uncertainty with age compared to $^{36}$Cl. The relative uncertainty of the effective $^{36}$Cl/$^{10}$Be ratio half-life is only 1.1% and is negligible in comparison to the measurement uncertainty.

The real challenge, however, of dating with the $^{36}$Cl/$^{10}$Be ratio is understanding the variability that obscures the radioactive decay signal. Some values in Fig. 3 are located on the expected decay curve and would return an accurate age, while others are too high or too low and would suggest an incorrect age several 100 kyr off from the established age scale. Glacial samples appear less problematic, but the defined thresholds for preservation are empirical and do not provide absolute certainty that samples are free of $^{36}$Cl loss, making it difficult to study possible climate influences. Without the two samples from the Eemian, the decay corrected $^{36}$Cl/$^{10}$Be negatively correlates with the $\delta$D signal. If this relationship can be confirmed in an ice core completely unaffected by $^{36}$Cl loss, it may be possible to apply a climate correction to reduce the variability. A second challenge is post-depositional $^{10}$Be mobility, which is likely to be an issue in the bottom section of the BE-OIC ice core drilled at LDC and other cores as well, so the method would benefit from directing future research at this phenomenon. If mobility is the only concern, there must be depth or age dependent representative sample size. If, on the other hand, remineralisation occurs, the experimental extraction method may need refinement.

### 4. Conclusion

The decay corrected $^{36}$Cl/$^{10}$Be ratio in the LDC and EDC cores correlates well with the $Cl^-/Na^+$ ratio over the last deglaciation, which can be explained by $^{36}$Cl and $Cl^-$ preservation under glacial conditions, when high dust concentrations prevent the outgassing of $^{36}$Cl and $Cl^-$ as volatile HCl, while both are lost in interglacial conditions. Over a timespan of 900 kyr, the EDC radionuclide data exhibit a decay signal, which is in agreement with the physical half-life of the $^{36}$Cl/$^{10}$Be ratio within the uncertainty, when limiting the sample selection to glacial samples. Smaller deviations from an ideal decay curve may be related to the different transport and deposition pathways of $^{36}$Cl and $^{10}$Be, which are linked to their respective chemical and physical properties. Additionally, there are indications that $^{10}$Be concentrations may be affected by post-depositional mobilisation in the deepest ice, which changes the original distribution and is visible as an apparent $^{10}$Be loss in our limited number of samples.

To reconstruct the undisturbed $^{36}$Cl/$^{10}$Be ratio decay signal and achieve uncertainties close to those presented in Fig. 5, the climate-related $^{36}$Cl/$^{10}$Be variability as well as the post-depositional behaviour of $^{10}$Be need to be better understood. If these influences can be quantified, the $^{36}$Cl/$^{10}$Be ratio can be corrected and ice core age estimates can be improved.

### CRediT authorship contribution statement

**Niklas Kappelt:** Conceptualisation, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Visualisation, Writing – original draft, Writing – review & editing. **Raimund Muscheler:** Conceptualisation, Funding acquisition, Methodology, Resources, Supervision, Writing – review & editing. **Mélanie Baroni:** Conceptualisation, Data curation, Funding acquisition, Investigation, Methodology,
Resources, Writing – review & editing. **Juerg Beer:** Methodology, Writing – review & editing. **Marcus Christl:** Data curation, Investigation, Methodology, Resources, Writing – review & editing. **Christof Vockenhuber:** Data curation, Investigation, Methodology, Resources, Writing – review & editing. **Edouard Bard:** Funding acquisition, Resources, Writing – review & editing. **ASTER Team:** Data curation, Investigation, Methodology, Resources. **Eric Wolff:** Conceptualisation, Funding acquisition, Methodology, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Niklas Kappelt reports financial support was provided by European Commission. Niklas Kappelt reports financial support was provided by Royal Physiographic Society of Lund. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors thank Florian Adolphi for providing a Matlab script that was used for radionuclide production rate calculation according to Poluianov et al. and Grant Raisbeck, who shared his labs in Orsay with us for the first steps of the sample preparation. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 955750. This publication was generated in the frame of Beyond EPICA. The project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 815384 (Oldest Ice Core). It is supported by national partners and funding agencies in Belgium, Denmark, France, Germany, Italy, Norway, Sweden, Switzerland, The Netherlands and the United Kingdom. Logistic support is mainly provided by ENEA and IPEV through the Concordia Station system. The opinions expressed and arguments employed herein do not necessarily reflect the official views of the European Union funding agency or other national funding bodies. This is Beyond EPICA publication number 42.

Appendix A. Supplementary data

Supplementary material related to this article can be found online
at https://doi.org/10.1016/j.quascirev.2025.109254.

Data availability

The radionuclide data are available at zenodo.org via https://doi.
org/10.5281/zenodo.14209851 with license Creative Commons Attri-
bution 4.0 International.

References

Adolphi, F., Muscheler, R., Svensson, A., Aldahan, A., Possnert, G., Beer, J., Sjolte, J., Björck, S., Matthes, K., Thiéblemont, R., 2014. Persistent link between solar activity and Greenland climate during the Last Glacial Maximum. Nat. Geosci. 7 (9), 662–666. http://dx.doi.org/10.1038/ngeo2225.

Auer, M., Wagenbach, D., Wild, E.M., Wallner, A., Priller, A., Miller, H., Schlosser, C., Kutschera, W., 2009. Cosmogenic 26Al in the atmosphere and the prospect of a 26Al/10Be chronometer to date old ice. Earth Planet. Sci. Lett. 287 (3–4), 453–462.
http://dx.doi.org/10.1016/j.epsl.2009.08.030.

Baglin, C.M., 2008. Nuclear data sheets for A = 81. Nucl. Data Sheets 109 (10), 2257–2437. http://dx.doi.org/10.1016/j.nds.2008.09.001.

Baroni, M., Bard, E., Petit, J.R., Viseur, S., 2019. Persistent draining of the stratospheric 10Be reservoir after the Samalas Volcanic Eruption (1257 CE). J. Geophys. Res.: Atmos. 124 (13), 7082–7097. http://dx.doi.org/10.1029/2018JD029823.

Baumgartner, S., Beer, J., Masarik, J., Wagner, G., Meynadier, L., Synal, H.-A., 1998. Geomagnetic modulation of the 36Cl flux in the GRIP ice core, greenland. Science 279 (5355), 1330–1332. http://dx.doi.org/10.1126/science.279.5355.1330.

Baumgartner, S., Beer, J., Suter, M., Dittrich-Hannen, B., Synal, H.-A., Kubik, P.W., Hammer, C., Johnsen, S., 1997a. Chlorine 36 fallout in the summit greenland ice core project ice core. J. Geophys. Res.: Ocean. 102 (C12), 26659–26662. http://dx.doi.org/10.1029/97JC00166.

Baumgartner, S., Beer, J., Wagner, G., Kubik, P., Suter, M., Raisbeck, G., Yiou, F., 1997b. 10Be and dust. Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms 123 (1-4), 296-301. http://dx.doi.org/10.1016/S0168-583X(96) 00751-3.

Benassai, S., Becagli, S., Gragnani, R., Magand, O., Proposito, M., Fattori, I., Traversi, R., Udisti, R., 2005. Sea-spray deposition in Antarctic coastal and plateau areas from ITASE traverses. Ann. Glaciol. 41, 32–40. http://dx.doi.org/10.3189/ 172756405781813285.

Beyond EPICA Consortium, 2023. Beyond EPICA web page.

Bouchet, M., Landais, A., Grisart, A., Parrenin, F., Prié, F., Jacob, R., Fourré, E., Capron, E., Raynaud, D., Lipenkov, V.Y., Loutre, M.-F., Extier, T., Svensson, A., Legrain, E., Martinerie, P., Leuenberger, M., Jiang, W., Ritterbusch, F., Lu, Z.-T., Yang, G.-M., 2023. The Antarctic Ice Core Chronology 2023 (AICC2023) chronological framework and associated timescale for the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core. Clim. the Past 19 (11), 2257–2286. http://dx.doi.org/10.5194/cp-19-2257-2023.

Braucher, R., Guillou, V., Bourlès, D.L., Arnold, M., Aumaitre, G., Keddadouche, K., Nottoli, E., 2015. Preparation of ASTER in-house 10Be/9Be standard solutions. Nucl. Instruments Methods Phys. Res. Sect. B: Beam Interactions Mater. Atoms 361, 335–340. http://dx.doi.org/10.1016/j.nimb.2015.06.012.

Channell, J.E., Xuan, C., Hodell, D.A., 2009. Stacking paleointensity and oxygen isotope data for the last 1.5 Myr (PISO-1500). Earth Planet. Sci. Lett. 283 (1-4), 14-23. http://dx.doi.org/10.1016/j.epsl.2009.03.012.

Chappellaz, J., Brook, E., Blunier, T., Malaizé, B., 1997. CH4 and δ18O of O2 records from Antarctic and Greenland ice: A clue for stratigraphic disturbance in the bottom part of the Greenland Ice Core Project and the Greenland Ice Sheet Project 2 ice cores. J. Geophys. Res.: Ocean. 102 (C12), 26547–26557. http://dx.doi.org/10.1029/97JC00164.

Chmeleck, J., von Blanckenburg, F., Kossert, K., Jakob, D., 2010. Determination of the 10Be half-life by multicollector ICP-MS and liquid scintillation counting. Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interactions Mater. Atoms 268 (2), 192–199. http://dx.doi.org/10.1016/j.nimb.2009.09.012.

Christl, M., Vockenhuber, C., Kubik, P., Wacker, L., Lachner, J., Alfimov, V., Synal, H.-A., 2013. The ETH Zurich AMS facilities: Performance parameters and reference materials. Nucl. Instruments Methods Phys. Res. Sect. B: Beam Interactions Mater. Atoms 294, 29–38. http://dx.doi.org/10.1016/j.nimb.2012.03.004.

Crotti, I., Landais, A., Stenni, B., Bazin, L., Parrenin, F., Frezzotti, M., Ritterbusch, F., Lu, Z.-T., Jiang, W., Yang, G.-M., Fourré, E., Orsi, A., Jacob, R., Minster, B., Prié, F., Dreossi, G., Barbante, C., 2021. An extension of the TALDICE ice core age scale reaching back to MIS 10.1. Quat. Sci. Rev. 266, 107078. http://dx.doi.org/10.1016/
j.quascirev.2021.107078.

Delmas, R.J., Beer, J., Synal, H.A., Muscheler, R., Petit, J.R., Pourchet, M., 2004. Bomb-
test 36Cl measurements in Vostok snow (Antarctica) and the use of 36Cl as a dating
tool for deep ice cores. Tellus, Ser. B: Chem. Phys. Meteorol. 56 (5), 492-498.
http://dx.doi.org/10.1111/j.1600-0889.2004.00109.x.

Diehl, K., Mitra, S.K., Pruppacher, H.R., 1995. A laboratory study of the uptake of HNO3 and HCl vapor by snow crystals and ice spheres at temperatures between 0 and -40°C. Atmos. Environ. 29 (9), 975-981. http://dx.doi.org/10.1016/1352-2310(95)00022-Q.

EKaykin, A.A., Lipenkov, V.Y., Barkov, N.I., Petit, J.R., Masson-Delmotte, V., 2002. Spatial and temporal variability in isotope composition of recent snow in the vicinity of Vostok station, Antarctica: implications for ice-core record interpretation. Ann. Glaciol. 35, 181–186. http://dx.doi.org/10.3189/172756402781617626.

Elmore, D., Tubbs, L.E., Newman, D., Ma, X.Z., Finkel, R., Nishiizumi, K., Beer, J., Oeschger, H., Andree, M., 1982. 36Cl bomb pulse measured in a shallow ice core from Dye 3, Greenland. Nature 300 (5894), 735–737. http://dx.doi.org/10.1038/300735a0.

Endt, P., van dêr Leun, C., 1973. Energy levels of A = 21-44 nuclei (V). Nucl. Phys. A 214 (C), 1-625. http://dx.doi.org/10.1016/0375-9474(73)91131-7.

EPICA Community Members, 2004. Eight glacial cycles from an Antarctic ice core. Nature 429 (6992), 623–628. http://dx.doi.org/10.1038/nature02599.

Fuchs, A., Leuenberger, M.C., 1996. δ18O of atmospheric oxygen measured on the GRIP Ice Core Document Stratigraphic disturbances in the lowest 10% of the core. Geophys. Res. Lett. 23 (9), 1049–1052. http://dx.doi.org/10.1029/96GL00588.

Grootes, P.M., Stuiver, M., White, J.W.C., Johnsen, S., Jouzel, J., 1993. Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores. Nature 366 (6455), 552–554. http://dx.doi.org/10.1038/366552a0.

Heikkilä, U., Beer, J., Abreu, J.A., Steinhilber, F., 2013. On the atmospheric transport and deposition of the cosmogenic radionuclides (10Be): A review. Space Sci. Rev. 176 (1-4), 321–332. http://dx.doi.org/10.1007/s11214-011-9838-0.
Heikkilä, U., Beer, J., Feichter, J., 2009a. Meridional transport and deposition of atmospheric 10Be. Atmospheric Chem. Phys. 9 (2), 515–527. http://dx.doi.org/10.5194/acp-9-515-2009.

Heikkilä, U., Beer, J., Feichter, J., Alfimov, V., Synal, H.-A., Schotterer, U., Eichler, A., Schwikowski, M., Thompson, L., 2009b. 36Cl bomb peak: comparison of modeled and measured data. Atmospheric Chem. Phys. 9 (12), 4145–4156. http://dx.doi.org/10.5194/acp-9-4145-2009.

Heikkilä, U., Smith, A.M., 2013. Production rate and climate influences on the variability of 10 Be deposition simulated by ECHAM5-HAM: Globally, in Greenland, and in Antarctica. J. Geophys. Res.: Atmos. 118 (6), 2506–2520. http://dx.doi.org/10.1002/jgrd.50217.

Herbst, K., Muscheler, R., Heber, B., 2017. The new local interstellar spectra and their influence on the production rates of the cosmogenic radionuclides 10Be and 14C. J. Geophys. Res.: Space Phys. 122 (1), 23–34. http://dx.doi.org/10.1002/2016JA023207.

Jouzel, J., Masson-Delmotte, V., Cattani, O., Dreyfus, G., Falourd, S., Hoffmann, G., Minster, B., Nouet, J., Barnola, J.M., Chappellaz, J., Fischer, H., Gallet, J.C., Johnsen, S., Leuenberger, M., Loulergue, L., Luethi, D., Oerter, H., Parrenin, F., Raisbeck, G., Raynaud, D., Schilt, A., Schwander, J., Selmo, E., Souchez, R., Spahni, R., Stauffer, B., Steffensen, J.P., Stenni, B., Stocker, T.F., Tison, J.L., Werner, M., Wolff, E.W., 2007. Orbital and millennial antarctic climate variability over the past 800,000 years. Science 317 (5839), 793–796. http://dx.doi.org/10.1126/science.1141038.

Kanzawa, K., Miyake, F., Horiuchi, K., Sasa, K., Takano, K., Matsumura, M., Takahashi, T., Motizuki, Y., Takahashi, K., Nakai, Y., Ohtani, K., Tada, Y., Ochiai, Y., Motoyama, H., Matsuzaki, H., Yamazaki, A., Muramatsu, Y., Yamagata, T., 2021. High-resolution 10 Be and 36 Cl data from the Antarctic Dome Fuji ice core (100 years around 5480 BCE): An unusual grand solar minimum occurrence? J. Geophys. Res.: Space Phys. 126 (10), http://dx.doi.org/10.1029/2021JA029378.

Lal, D., 2007. Recycling of cosmogenic nuclides after their removal from the atmosphere; special case of appreciable transport of 10Be to polar regions by aeolian dust. Earth Planet. Sci. Lett. 264 (1–2), 177–187. http://dx.doi.org/10.1016/j.epsl.2007.09.030.

Legrand, M.R., Delmas, R.J., 1988. Formation of HCl in the Antarctic atmosphere. J. Geophys. Res.: Atmos. 93 (D6), 7153–7168. http://dx.doi.org/10.1029/JD093ID06p07153.

Legrand, M., Preunkert, S., Weller, R., Zipf, L., Elsässer, C., Merchel, S., Rugel, G., Wagenbach, D., 2017a. Year-round record of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) - Part 2: Biogenic sulfur (sulfate and methanesulfonate) aerosol. Atmospheric Chem. Phys. 17 (22), 14055–14073. http://dx.doi.org/10.5194/acp-17-14055-2017.

Legrand, M., Preunkert, S., Wolff, E., Weller, R., Jourdain, B., Wagenbach, D., 2017b. Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) - Part 1: Fractionation of sea-salt particles. Atmospheric Chem. Phys. 17 (22), 14039–14054. http://dx.doi.org/10.5194/acp-17-14039-2017.

Lukasczyk, C.E., 1994. 36Chlor in Grönlandeis (Ph.D. thesis). ETH Zürich, Zürich, http://dx.doi.org/10.3929/ethz-a-000965554.

Lyman, J., Fleming, R.H., 1940. Composition of seawater. J. Mar. Res. 3 (2), 134–146.

Muscheler, R., 2000. Nachweis von Änderungen im Kohlenstoffkreislauf durch Vergleich der Radionuklide 10Be, 36Cl und 14C (Ph.D. thesis). ETH Zürich, Zürich, http://dx.doi.org/10.3929/ethz-a-004179578.

Muscheler, R., Adolphi, F., Herbst, K., Nilsson, A., 2016. The revised sunspot record in comparison to cosmogenic radionuclide-based solar activity reconstructions. Sol. Phys. 291 (9–10), 3025–3043. http://dx.doi.org/10.1007/s11207-016-0969-z.

Muscheler, R., Beer, J., Kubik, P.W., Synal, H.A., 2005. Geomagnetic field intensity during the last 60,000 years based on 10Be and 36Cl from the Summit ice cores and 14C. Quat. Sci. Rev. 24 (16–17), 1849–1860. http://dx.doi.org/10.1016/j.quascirev.2005.01.012.

Muscheler, R., Beer, J., Wagner, G., Laj, C., Kissel, C., Raisbeck, G.M., Yiou, F., Kubik, P.W., 2004. Changes in the carbon cycle during the last deglaciation as indicated by the comparison of 10Be and 14C records. Earth Planet. Sci. Lett. 219 (3–4), 325–340. http://dx.doi.org/10.1016/S0012-821X(03)00722-2.

Nguyen, L., Suttie, N., Nilsson, A., Muscheler, R., 2022. A novel Bayesian approach for disentangling solar and geomagnetic field influences on the radionuclide production rates. Earth, Planets Space 74 (1), 1–19. http://dx.doi.org/10.1186/s40623-022-01688-1.

Nilsson, A., Nguyen, L., Panovska, S., Herbst, K., Zheng, M., Suttie, N., Muscheler, R., 2024. Holocene solar activity inferred from global and hemispherical cosmic-ray proxy records. Nat. Geosci. 17 (7), 654–659. http://dx.doi.org/10.1038/s41561-024-01467-5.

Nishizumi, K., Imamura, M., Caffee, M.W., Southon, J.R., Finkel, R.C., McAnchin, J., 2007. Absolute calibration of 10Be AMS standards. Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms 258 (2), 403–413. http://dx.doi.org/10.1016/j.nimb.2007.01.297.

Parrenin, F., Barnola, J.M., Beer, J., Blunier, T., Castellano, E., Chappellaz, J., Dreyfus, G., Fischer, H., Fujita, S., Jouzel, J., Kawamura, K., Lemieux-Dudon, B., Loulergue, L., Masson-Delmotte, V., Narcisi, B., Petit, J.R., Raisbeck, G., Raynaud, D., Ruth, U., Schwander, J., Severi, M., Spahni, R., Steffensen, J.P., Svensson, A., Udisti, R., Waelbroeck, C., Wolff, E., 2007. The EDC3 chronology for the EPICA Dome C ice core. Clim. Past 3 (3), 485–497. http://dx.doi.org/10.5194/cp-3-485-2007.

Pedro, J.B., Heikkilä, U.E., Klekociuk, A., Smith, A.M., Van Ommen, T.D., Curran, M.A., 2011. Beryllium-10 transport to Antarctica: Results from seasonally resolved observations and modeling. J. Geophys. Res. Atmos. 116 (23), 1–14. http://dx.doi.org/10.1029/2011JD016530.

Pivot, S., Baroni, M., Bard, E., Giraud, X., 2019. A comparison of 36Cl nuclear bomb inputs deposited in snow from Vostok and Talos Dome, Antarctica, using the 36Cl/Cl ratio. J. Geophys. Res.: Atmos. 124 (20), 10973–10988. http://dx.doi.org/10.1029/2018JD030200.

Poluianov, S., Kovaltsov, G.A., Mishev, A.L., Usoskin, I.G., 2016. Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions. J. Geophys. Res.: Atmos. 121, 8125–8136. http://dx.doi.org/10.1002/2016JD025034.

Raisbeck, G., Yiou, F., 1985. 10Be in polar ice and atmospheres. Ann. Glaciol. 7, 138–140. http://dx.doi.org/10.3189/s026030550006054.

Raisbeck, G.M., Yiou, F., Cattani, O., Jouzel, J., 2006. 10Be evidence for the Matuyama–Brunhes geomagnetic reversal in the EPICA Dome C ice core. Nature 444 (7115), 82–84. http://dx.doi.org/10.1038/nature05266.

Raisbeck, G.M., Yiou, F., Fruneau, M., Loiseaux, J.M., Lieuvin, M., Ravel, J.C., 1981. Cosmogenic 10Be/7Be as a probe of atmospheric transport processes. Geophys. Res. Lett. 8 (9), 1015–1018. http://dx.doi.org/10.1029/GL008i009p01015.

Rankin, A.M., Wolff, E.W., Mulvaney, R., 2004. A reinterpretation of sea-salt records in Greenland and Antarctic ice cores? Ann. Glaciol. 39, 276–282. http://dx.doi.org/10.3189/172756404781814681.

Röthlisberger, R., Hutterli, M.A., Wolff, E.W., Mulvaney, R., Fischer, H., Bigler, M., Goto-Azuma, K., Hansson, M.E., Ruth, U., Siggaard-Andersen, M.-L., Steffensen, J.P., 2002. Nitrate in Greenland and Antarctic ice cores: a detailed description of post-depositional processes. Ann. Glaciol. 35, 209–216. http://dx.doi.org/10.3189/172756402781817220.

Röthlisberger, R., Mulvaney, R., Wolff, E.W., Hutterli, M.A., Bigler, M., de Angelis, M., Hansson, M.E., Steffensen, J.P., Udisti, R., 2003. Limited dechloration of sea-salt aerosols during the last glacial period: Evidence from the European project for ice coring in Antarctica (EPICA) Dome C ice core. J. Geophys. Res.: Atmos. 108 (16), 1–6. http://dx.doi.org/10.1029/2003jd003604.

Rowell, I.F., 2022. New Ice Core Records from West Antarctica and Their Spatial Context: from 1000 to 100,000 Years (Ph.D. thesis). (August), University of Cambridge, http://dx.doi.org/10.17863/CAM.94392.

Rowell, I.F., Mulvaney, R., Rix, J., Tetzner, D.R., Wolff, E.W., 2023. Viability of chemical and water isotope ratio measurements of RAID ice chippings from Antarctica. J. Glaciol. 69 (275), 623–638. http://dx.doi.org/10.1017/jog.2022.94.

Ruth, U., Barnola, J.M., Beer, J., Bigler, M., Blunier, T., Castellano, E., Fischer, H., Fundel, F., Huybrechts, P., Kaufmann, P., Kipfstuhl, S., Lambrecht, A., Morganti, A., Oerter, H., Parrenin, F., Rybak, O., Severi, M., Udisti, R., Wilhelms, F., Wolff, E., 2007. “EDMLI”: A chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years. Clim. Past 3 (3), 475–484. http://dx.doi.org/10.5194/cp-3-475-2007.

Schwander, J., Jouzel, J., Hammer, C.U., Petit, J.-R., Udisti, R., Wolff, E., 2001. A tentative chronology for the EPICA Dome Concordia Ice Core. Geophys. Res. Lett. 28 (22), 4243–4246. http://dx.doi.org/10.1029/2000GL011981.

Synal, H.-A., Beer, J., Bonani, G., Suter, M., Wöllfi, W., 1990. Atmospheric transport of bomb-produced 36Cl. Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interact. Mater. Atoms 52 (3–4), 483–488. http://dx.doi.org/10.1016/0168-583X(90)90462-4.

Thibert, E., Dominé, F., 1998. Thermodynamics and kinetics of the solid solution of HNO3 in ice. J. Phys. Chem. B 102 (22), 4432–4439. http://dx.doi.org/10.1021/jp980569a.

Veres, D., Bazin, L., Landais, A., Toyé Mahamadou Kele, H., Lemieux-Dudon, B., Parrenin, F., Martinerie, P., Blayo, E., Blunier, T., Capron, E., Chappellaz, J., Rasmussen, S.O., Severi, M., Svensson, A., Vinther, B., Wolff, E.W., 2013. The Antarctic Ice Core Chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years. Clim. Past 9 (4), 1733–1748. http://dx.doi.org/10.5194/cp-9-1733-2013.

Wagner, G., Beer, J., Masarik, J., Muscheler, R., Kubik, P.W., Mende, W., Laj, C., Raisbeck, G.M., Yiou, F., 2001. Presence of the solar de vries cycle (205 years) during the last ice age. Geophys. Res. Lett. 28 (2), 303–306. http://dx.doi.org/10.1029/2000GL006116.

Wagner, G., Masarik, J., Beer, J., Baumgartner, S., Imboden, D., Kubik, P.W., Synal, H.A., Suter, M., 2000. Reconstruction of the geomagnetic field between 20 and 60 kyr BP from cosmogenic radionuclides in the GRIP ice core. Nucl. Instrum. Methods Phys. Res. Sect. B: Beam Interactions Mater. Atoms 172 (1–4), 597–604. http://dx.doi.org/10.1016/S0168-583X(00)00285-8.
Wagnon, P., Delmas, R.J., Legrand, M., 1999. Loss of volatile acid species from upper firn layers at Vostok, Antarctica. J. Geophys. Res. Atmospheres 104 (D3), 3423–3431. http://dx.doi.org/10.1029/98JD02855.

Wolff, E.W., Barbante, C., Becagli, S., Bigler, M., Boutron, C.F., Castellano, E., de Angelis, M., Federer, U., Fischer, H., Fundel, F., Hansson, M., Hutterli, M., Jonsell, U., Karlin, T., Kaufmann, P., Lambert, F., Littot, G.C., Mulvaney, R., Röthlisberger, R., Ruth, U., Severi, M., Siggaard-Andersen, M.L., Sime, L.C., Steffensen, J.P., Stocker, T.F., Traversi, R., Twarloh, B., Udisti, R., Wagenbach, D., Wegner, A., 2010. Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core. Quat. Sci. Rev. 29 (1–2), 285–295. http://dx.doi.org/10.1016/j.quascirev.2009.06.013.

Yiou, F., Raisbeck, G.M., Baumgartner, S., Beer, J., Hammer, C., Johnsen, S., Jouzel, J., Kubik, P.W., Lestringuez, J., Stiévenard, M., Suter, M., Yiou, P., 1997. Beryllium 10 in the greenland ice core project ice core at summit, greenland. J. Geophys. Res.: Ocean. 102 (C12), 26783–26794. http://dx.doi.org/10.1029/97JC01265.

Zerle, L., Faestermann, T., Knie, K., Korschinek, G., Nolte, E., Beer, J., Schot-
terer, U., 1997. The 41Ca bomb pulse and atmospheric transport of radionuclides.
J. Geophys. Res. Atmos. 102 (16), 19517–19527. http://dx.doi.org/10.1029/
97jd00701.

Zheng, M., Sturevik-Storm, A., Nilsson, A., Adolphi, F., Aldahan, A., Possnert, G., Muscheler, R., 2021. Geomagnetic dipole moment variations for the last glacial period inferred from cosmogenic radionuclides in Greenland ice cores via disen-tangling the climate and production signals. Quat. Sci. Rev. 258, http://dx.doi.org/10.1016/j.quascirev.2021.106881.