Is the penultimate deglaciation (Termination II) recorded in the folded ice in the deepest part of the Greenland NEEM ice core?

The folded stratigraphy of the ice between 2432.2 and 2540 m in the Greenland NEEM ice core precludes direct access to climatic information older than 128.5 ka b2k (thousands of years before 2000 CE) (NEEM comm. Members, 2013). The disturbed stratigraphy is particularly unfortunate because this ice’s age corresponds to the Termination II (140–130 ka b2k). The climatic transition from the penultimate glacial period (MIS 6, 190–130 ka b2k) to the last interglacial (MIS 5e, 130–120 ka b2k) has not yet been extracted from Greenlandic ice core records.

In this study, we propose a possible reconstruction of the disturbed NEEM stratigraphy spanning the MIS 6–MIS 5e transition based on the succession of globally well-mixed gas parameters. The NEEM δ¹⁸O_ice chronological sequence is obtained by comparing a new set of δ¹⁸O of atmospheric O₂ and CH₄ measurements from the bottom section of the NEEM core with their counterpart in composite Antarctic records. The proposed stratigraphy is also discussed with respect to three radiometric ages estimated from new ⁸¹Kr measurements from the bottom part of the NEEM core. The new gas measurements suggest that disturbed ice below 2432.2 m in the NEEM ice core contains, stratigraphically intact, but folded ice, with climatic information from MIS 6 and MIS 5e, possibly from the penultimate deglaciation, and that sections of MIS 5e are present twice in the ice.