UC Santa Barbara

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 (δ13CP- NA/2 correlates well with pCO2. δ13CP-NA/2 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. δ13C P- NA/2 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. © 2010 by the American Geophysical Union.