The first coarse-resolution Beyond EPICA CO2 record covering the Mid-Pleistocene Transition: Insights from long-term carbon-cycle dynamics

The Mid-Pleistocene Transition (MPT; 1.25 – 0.8 Myr) marks a transition from the “41-kyr world”, in which the Earth alternated between cold and warm periods about every 41,000 years, to the “100-kyr world” in which the Earth remained predominantly under glacial conditions but was punctuated every 80,000 to 120,000 years by interglacial periods. Variations in orbital forcing, the “pacemaker of the ice ages”, are stable across the MPT and thus cannot be invoked as a driver of this transition. Thus, most hypotheses call upon a forcing that drives a secular change, a feedback in the Earth system that changes/emerges, or a combination of the two.

One hypothesis for the MPT suggests that a long-term decline in (glacial) atmospheric CO₂ levels led to a cooling, facilitating the formation of extensive ice sheets in North America and a sea-level drop of approximately 70 m (Bintanja & van de Wal, 2008). Accordingly, decreasing atmospheric CO₂ concentration may have played a central role in driving this global cooling. Despite recent advances in marine and ice core CO₂ reconstructions (Nuber et al., 2025; Marks Peterson et al., 2025) the change of greenhouse gas forcing across the MPT remains uncertain for CO₂.

In order to investigate the role of atmospheric CO₂ across the MPT, greenhouse gases and the stable carbon isotopic composition of CO₂ (δ¹³C-CO₂) were measured on discrete ice core samples from the Beyond EPICA ice core. For this purpose, a coupled Laser induced sublimation extraction – Quantum Cascade laser Absorption Spectrometer (LISE-QCLAS) was used, allowing the simultaneous and semi-continuous extraction and measurement of CO₂, CH₄ and N₂O as well as δ¹³C-CO₂ on air samples of only 1 – 2 mL, corresponding to 10 – 15 g of ice.

This talk will present the first ice core data capable of capturing glacial–interglacial variations in atmospheric CO₂ across the MPT. Additionally, we will present the first unconditionally pristine measurements of δ¹³C-CO₂ during the 41-kyr world. These data will allow us to explore the underlying biogeochemical processes that may be responsible for the new modes of atmospheric CO₂ variability we have observed.