Orbital Dating of the Beyond EPICA Ice Core and Identification of Possible Stratigraphic Disturbances

The new Beyond EPICA Antarctic ice core plays a crucial role in deciphering the contribution and behaviour of atmospheric proxies before and during the Mid-Pleistocene transition. In order to fully understand and correctly interpret the connection between different proxies both from the ice and gas phase of the ice core, as well as from other climactic archives, an accurate chronology of the entire ice core is needed. This can be achieved with orbital dating, exploiting the unique relationship between insolation and some of the isotopic and elemental ratios of atmospheric constituents such as nitrogen, oxygen, and argon of the air bubbles trapped in the ice. Using new atmospheric δ¹⁸O of O₂, δ(O₂/N₂), and δ(Ar/N₂) data in the depth range between 2400-2507 m from the Beyond EPICA ice core, we propose new chronological tie points, which are independent of alignment to marine archives, for the construction of a gas and ice chronology of the Beyond EPICA ice core before 800,000 years before present.

Additionally, δ¹⁵N of N₂ measurements provide a way to quantify variations in the lock-in depth and the age difference between the ice and the gas phase (Δage) over the entire time period covered by the Beyond EPICA ice core. The new δ¹⁵N dataset provided here is key for the coherence between the ice and gas timescale. Moreover, we use the expected depth difference (Δdepth) between the same event recorded in the ice phase (through δD or δ¹⁸O of the ice) and in the gas phase (through δ¹⁵N of N₂) as a test for the integrity of the stratigraphy: a concomitant change in δD or δ¹⁸O of the ice and δ¹⁵N of N₂ may be the signature of an ice hiatus or folding event.