Southern Ocean abyssal oxygenation linked to the air-sea partitioning of carbon throughout the last glacial cycle

Abstract:

Although no single mechanism can account for the full amplitude of past atmospheric CO₂ variability over glacial interglacial cycles, a build-up of biologically-stored carbon in the deep ocean has emerged as a central mechanism for low CO₂ during the Last Glacial Maximum (LGM). However, the mechanisms for which this deeply sequestered carbon was released, and the relative importance it played in the history of atmospheric CO₂ prior to the LGM, remain subjects of debate. Here, we present new redox-sensitive trace metal records from the Antarctic Zone of the Southern Ocean that provide an unprecedented reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our results show that respired carbon was removed from the abyssal Southern Ocean during the northern hemisphere cold phases of the deglaciation, when atmospheric CO₂ rose rapidly, due to a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our new records show that the correlation between atmospheric CO₂ and abyssal Southern Ocean oxygenation was maintained throughout most of the prior 80 kyrs, consistent with a unifying role of the Southern Ocean through a coupled control on deep ocean circulation and iron fertilization.