Evaluating the Glacial‐Deglacial Carbon Respiration and Ventilation Change Hypothesis as a Mechanism for Changing Atmospheric CO 2

The prevailing hypothesis to explain pCO 2 rise at the last glacial termination calls upon enhanced ventilation of excess respired carbon that accumulated in the deep sea during the glacial. Recent studies argue lower [O 2 ] in the glacial ocean is indicative of increased carbon respiration. The magnitude of [O 2 ] depletion was 100–140 µ mol/kg at the glacial maximum. Because respiration is coupled to δ 13 C of dissolved inorganic carbon (DIC), [O 2 ] depletion of 100–140 µ mol/kg from carbon respiration would lower deep water δ 13 C DIC by ∼1‰ relative to surface water. Prolonged sequestration of respired carbon would also lower the amount of 14 C in the deep sea. We show that Pacific Deep Water δ 13 C DIC did not decrease relative to the surface ocean and Δ 14 C was only ∼50‰ lower during the late glacial. Model simulations of the hypothesized ventilation change during deglaciation lead to large increases in δ 13 C DIC , Δ 14 C, and ε 14 C that are not recorded in observations.