The Southern Ocean mechanism of the Late Pleistocene glacial cycling and its implications for the formation of the northern hemisphere ice sheet

It has been generally believed that the Southern Ocean has played an important role in modulating glacial/interglacial changes of the atmospheric partial pressure of carbon dioxide (pCO₂) during the Late Pleistocene. In the late Pleistocene, the atmospheric pCO₂ during the glacial periods was about 90×10⁻⁶ lower than that during the interglacial periods. Furthermore, in around 2.7 Ma, with the intensification of the Northern Hemisphere Glaciation (iNHG), the amplitude of glacial cycles increased, while the atmospheric pCO₂ greatly decreased. Exploring the reasons for the decline in atmospheric pCO₂ during the Late Pleistocene glaciation and the iNHG period is of great significance for constructing a complete theory of the Ice Ages. We combined the records of ocean currents, sea ice, and productivity in the Subantarctic Antarctic Zone (SAZ) in the northern part of the Southern Ocean and the Antarctic Zone (AZ) in the southern part of the Southern Ocean during the Late Pleistocene glaciation, investigated the possible carbon storage mechanisms in these two regions during this period, and discussed the changes in the Southern Ocean currents and carbon reservoirs during the iNHG period by integrating geological records. We proposed that SAZ and AZ had different carbon storage mechanisms during ice ages. The enhancement of iron fertilization increased the biological pump efficiency in the SAZ, thus increasing ocean carbon sequestration. Meanwhile, in the AZ, weakened deep-water ventilation, sea ice expansion, and enhanced deep-sea stratification were the key mechanisms for enhancing deep-sea carbon sequestration. Additionally, records of ocean currents and carbon reservoirs during the iNHG period indicate that southern ocean sourced waters expanded significantly towards the deep North Atlantic and North Pacific, with an expansion of sea ice in the Southern Ocean, enhancement in iron fertilization, and the increase in the Pacific carbon reservoir. We infer that the Southern Ocean mechanisms of the Late Pleistocene ice glacial cycling had probably contributed greatly to the decrease in the atmospheric pCO₂ during the period of the iNHG, which triggered the final formation of the northern hemisphere glaciation.