Fig. 2: Phase-relationship between δ¹³C and δ¹⁸O on 100-kyr eccentricity time-scales.

On eccentricity time-scales, δ¹³C and δ¹⁸O exhibit cyclic in-phase behaviour from 35 till ~6 Ma in the Pacific, as well as in the Atlantic Ocean (Intervals I and II). Around 6 Ma in the Pacific (Interval III), and somewhat later in the Atlantic, we observe an abrupt shift from in-phase to anti-phase behaviour. The plotted uncertainty bar indicates a typical confidence interval (CI) on the phase estimate of ±0.44 rad. Uncertainty on the phase difference between δ¹³C and δ¹⁸O is inversely proportional to coherence and overall ranges between ±0.25 and ±0.59 rad. Antarctic and Arctic ice volume reconstructions are from Oerlemans⁶³ and Berger et al. ⁸⁰, respectively. The earlier onset of NH glaciation suggested by this study is indicated in red. Atmospheric CO₂ reconstruction from Zhang et al. ⁸¹. Grey triangles indicate opening and closing of important ocean gateways. BS, Bering Strait; FS, Fram Strait; Drake, Drake Passage; CAS, Central American Seaway; ITF, Indonesian Throughflow. All Sites that constitute the δ¹³C megasplice are included here (references in Fig. 1) and are complemented by additional orbital-resolution benthic isotope data from Sites 926⁸², 982⁸³, 1264/1265^15,49, U1334^50,84, U1337¹⁷ and U1338^6,85 (data as time-series in Supplementary Fig. 3).