Evaluating the Glacial-Deglacial Carbon Respiration and Ventilation Change Hypothesis as a Mechanism for Changing Atmospheric CO₂

The prevailing hypothesis to explain pCO₂ 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 [O₂] in the glacial ocean is indicative of increased carbon respiration. The magnitude of [O₂] depletion was 100–140 µ mol/kg at the glacial maximum. Because respiration is coupled to δ¹³C of dissolved inorganic carbon (DIC), [O₂] depletion of 100–140 µ mol/kg from carbon respiration would lower deep water δ¹³C_DIC by ∼1‰ relative to surface water. Prolonged sequestration of respired carbon would also lower the amount of ¹⁴C in the deep sea. We show that Pacific Deep Water δ¹³C_DIC did not decrease relative to the surface ocean and Δ¹⁴C was only ∼50‰ lower during the late glacial. Model simulations of the hypothesized ventilation change during deglaciation lead to large increases in δ¹³C_DIC, Δ¹⁴C, and ε¹⁴C that are not recorded in observations.