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 δ13CDIC 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 δ13CDIC 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 δ13CDIC, Δ14C, and ε14C that are not recorded in observations.

Plain Language Summary

The prevailing hypothesis to explain atmospheric CO2 variability during glacial/interglacial cycles assumes atmospheric CO2 was sequestered into the deep sea as respired metabolic carbon. Recent studies argue in support of this by suggesting lower oxygen concentrations in the deep Pacific during the glacial reflects increased oxidation of marine organic matter that promoted a larger accumulation of respired carbon. We show this interpretation is not validated by independent tests, including records of deep water δ13C and Δ14C.