Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO₂ rise

Abstract. The link between the atmospheric CO₂ level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO₂ fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO₂ and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global 3-D ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO₂ rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during early deglaciation is not only consistent with recorded atmospheric CO₂ but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ¹³C_CO2, and the reconstructed changes in the Pacific CaCO₃ saturation horizon.