OLDER DEEP NORTHEAST PACIFIC DURING THE LAST GLACIAL MAXIMUM FOLLOWED BY LATE DEGLACIAL CIRCULATION RESPONSE

Lower atmospheric CO₂ levels during the Last Glacial Maximum (19-27 kyr BP) were likely due to carbon storage in the deep ocean, while rising CO₂ during the last deglaciation (~8-18 kyr BP) has been linked to oceanic carbon release. Such a scenario implies deep Pacific circulation was more sluggish during the LGM, followed by progressively enhanced circulation during the deglaciation. Here we use foraminiferal stable isotopes and radiocarbon to reconstruct a high resolution ventilation age history for the deep NE Pacific from 8 to 32 kyr BP, extending the available record by more than 10 kyr. We find that ¹⁴C ventilation ages were higher during the LGM, due to either slower circulation or higher preformed ages of water entering the deep Pacific. We also find three major declines in ventilation age, one during the LGM (at ~22 kyr BP) and two during the deglaciation (at ~15 kyr BP and 13 kyr BP). The LGM event lacks contemporaneous changes in benthic δ¹⁸O and δ¹³C, so it likely reflects a change in preformed age, due to retreat of summer sea ice in the Southern Ocean. The deglacial events, on the other hand, are characterized by synchronous changes in Δ¹⁴C, δ¹⁸O and δ¹³C, indicating enhanced circulation at these times. Our data imply that the deep NE Pacific sequestered carbon during the LGM and released it during the deglaciation, but after the initial rise in atmospheric CO₂.