Measurements of the 36Cl/10Be ratio in the deep ice of Talos Dome (East Antarctic): applications to paleomagnetism and ice dating.

Cosmogenic nuclides such as beryllium-10 (¹⁰Be) and chlorine-36 (³⁶Cl) are valuable tools for dating deep ice cores and reconstructing paleomagnetic events. These nuclides are formed through interactions of target atoms in the atmosphere with galactic cosmic rays and deposited on ice sheets in aerosol form only and aerosol and gaseous forms for ¹⁰Be and ³⁶Cl, respectively. However, questions persist regarding the preservation of their production signals in deep ice cores. In particular, low snow accumulation rates favour H³⁶Cl migration and outgassing from the snowpack (Delmas et al., 2004; Pivot et al., 2019).

Here, we present new measurements of ¹⁰Be and ³⁶Cl in the Talos Dome ice core, focusing on periods older than 170 ka BP. When corrected from the radioactive decay of ³⁶Cl and ¹⁰Be, a ³⁶Cl/¹⁰Be ratio of 0.125 is observed, consistent with ratios observed during the last 700 years in the Talos Dome ice core. The ³⁶Cl/¹⁰Be ratio generally overestimate the reconstructed age compared to those expected from AICC2023 chronology (Bouchet et al., 2023). Thus, the consideration of climatic and chemical concentrations is necessary to correctly apply the ³⁶Cl/¹⁰Be ratio as a dating tool.

Additionally, ¹⁰Be and ³⁶Cl fluxes record past Earth magnetic field variations. We identify the Iceland Basin geomagnetic excursion around 190 ka as a clear stratigraphic marker, associated with a near doubling of the ¹⁰Be and ³⁶Cl fluxes compared to background levels. By contrast, evidence for the Pringle Falls excursion(s) is less apparent. This different observation suggests that only the most intense excursions can be recorded in East Antarctic ice cores. This conclusion is of importance for future consideration of Beyond EPICA ice samples for investigating excursions and inversions after 800 ka.

Overall, our findings underscore the good preservation of atmospheric cosmogenic nuclide signals in the Talos Dome ice core, reinforcing their utility for dating deep ice and investigating paleomagnetic events.