中—晚更新世南大洋深部氧化还原条件指示的垂向流通状况:以IODP 374航次U1524A孔为例OA

The redox conditions in the deep ocean are important parameters for diagnosing carbon storage/release in abyssal waters.After correcting the oxygen consumption by organic matter,deep-sea redox conditions are regulated mainly by deep-water ventilation.However,in most available studies,the decoupling between lateral and vertical ventilation was often ignored,but instead used this indicator to suggest the overall or lateral ventilation intensity,which may not be correct in sea areas with developed vertical ventilation(such as the Southern Ocean).To address this issue,we reconstructed the productivity(opal/Ti),redox conditions(Mn/Ti and Mo/Ti ratios),and lateral current strength(ln(Zr/Rb))from International Ocean Discovery Program Hole U1524A in the Ross Sea,Antarctica,dated to the Middle-Late Pleistocene in a glacial-interglacial framework established through physical parameters.Results demonstrate distinct glacial patterns.The glacial periods were characterized by weaker oxidation(suboxic conditions),lower productivity,and stronger lateral currents compared to the interglacial periods that had stronger oxidation(oxic conditions),higher productivity,and weaker lateral current.Comparing these records with the record of the intensity of the Antarctic Circumpolar Current(ACC),which represents the vertical upwelling of deep water of the Circumpolar Deep Water(CDW),the vertical ventilation was proposed to be the dominate process of deep-sea redox condition.The specific mechanism is that during the glacial periods,the westerlies moved northward,while the ACC weakened and sea ice expanded,which collectively suppressed CDW upwelling.The reduced vertical ventilation diminished deep-sea oxidation and carbon release to the atmosphere,and consequently decreased the atmospheric pCO2.These findings demonstrate that the Southern Ocean deep-sea redox conditions in the Middle-Late Pleistocene reflected the vertical ventilation,underscoring the importance of distinguishing between vertical and lateral ventilation to properly interpret deep-sea redox signals.