南大洋对北半球大冰期（NHG）大气pCO2降低的贡献：NHG成因的启示

北半球大冰期（NHG）是上新世-更新世之交全球性的变冷事件，其通过放大、同步和驱动机制对全球气候影响深远。针对NHG的成因提出了一系列假说（如构造活动、地球轨道、热带过程和大气CO2假说），但一直悬而未决；模拟结果表明，诸多假说中只有大气pCO2降低能独立、圆满地驱动NHG。然而，不清楚哪个大洋封存以及如何封存NHG大气丢失的CO2，这其中南大洋甚具潜力。项目以IODP 374航次在南极罗斯海钻取的U1524A孔为材料，通过沉积物生源组分、硅藻δ30Si和氧化还原敏感元素、黄铁矿δ34S重建3.3-2 Ma南大洋的生产力、深部流通状况和氧化还原条件。进一步，分析这些生物地化参数与大气pCO2的对应关系，确证与查明南大洋深部封存NHG大气丢失CO2的事实与机制。最后，将上述表层-深部生物地化的演化与NHG相关记录对比，揭示南大洋驱动NHG的过程，明确南大洋在NHG中的重要地位。

Northern Hemisphere glaciation (NHG), a global cooling event during the Pliocene-Pleistocene transition, exerted significant impacts on global climate by amplifying, pacing and driving mechanisms. The cause of NHG remains elusive although a series of hypotheses involved with tectonic activity, orbital configuration, tropical process and atmospheric CO2 have been proposed to address it. Simulation results suggest that only the atmospheric pCO2 decline claimed by ‘atmospheric CO2 hypothesis’ among these hypotheses is large enough to drive the NHG. However, it is still not known where and how the lost atmospheric CO2 was sequestered during the NHG. Thereinto, the deep Southern Ocean has the potential to store the reduced atmospheric CO2 with the form of respired CO2, but the evidence on it is lacking. Here surface productivity, deep ventilation and redox conditions in the Southern Ocean in the interval of 3.3-2 Ma are reconstructed by biogenic components, diatom δ30Si, and redox-sensitive elements and pyrite δ34S from sediments of Hole U1524A recovered during the International Ocean Discovery Program (IODP) 374 expedition. Furthermore, facts and controls on the sequestration of atmospheric CO2 in deep Southern Ocean during the NHG are confirmed and explored, respectively, by analyzing the correspondence between these biogeochemical parameters and atmospheric pCO2. Finally, the comparison of surface and deep biogeochemical evolution above with relevant NHG records is used to reveal the driving process of Southern Ocean on the NHG, thus confirming the significance of Souther Ocean in the NHG.