A benthic δ¹³C-based proxy for atmospheric pCO₂ over the last 1.5 Myr

[1] A high-resolution marine proxy for atmospheric pCO₂ is needed to clarify the phase lag between pCO₂ and marine climate proxies and to provide a record of orbital-scale pCO₂ variations before the oldest ice core measurement at 800 ka. Benthic δ¹³C data should record deep ocean carbon storage and, thus, atmospheric pCO₂. This study finds that a modified δ¹³C gradient between the deep Pacific and intermediate North Atlantic (Δδ¹³C_P−) correlates well with pCO₂. Δδ¹³C_P− reproduces characteristic differences between pCO₂ and ice volume during Late Pleistocene glaciations and indicates that pCO₂ usually leads terminations by 0.2–3.7 kyr but lags by 3–10 kyr during two “failed” terminations at 535 and 745 ka. Δδ¹³C_P− gradually transitions from 41- to 100-kyr cyclicity from 1.3–0.7 Ma but has no secular trend in mean or amplitude since 1.5 Ma. The minimum pCO₂ of the last 1.5 Myr is estimated to be 155 ppm at ∼920 ka.