A benthic δ 13 C‐based proxy for atmospheric pCO 2 over the last 1.5 Myr

A high‐resolution marine proxy for atmospheric pCO 2 is needed to clarify the phase lag between pCO 2 and marine climate proxies and to provide a record of orbital‐scale pCO 2 variations before the oldest ice core measurement at 800 ka. Benthic δ 13 C data should record deep ocean carbon storage and, thus, atmospheric pCO 2 . This study finds that a modified δ 13 C gradient between the deep Pacific and intermediate North Atlantic (Δ δ 13 C P − ) correlates well with pCO 2 . Δ δ 13 C P − reproduces characteristic differences between pCO 2 and ice volume during Late Pleistocene glaciations and indicates that pCO 2 usually leads terminations by 0.2–3.7 kyr but lags by 3–10 kyr during two “failed” terminations at 535 and 745 ka. Δ δ 13 C 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 pCO 2 of the last 1.5 Myr is estimated to be 155 ppm at ∼920 ka.