南塔斯曼海隆2Ma以来碳酸钙沉积记录及其对环流系统和轨道周期的响应

南大洋CaCO3沉积在记录生物泵调节大气CO2的同时,也记录了南大洋表层锋面系统和深部环流格局的重要转变.通过南塔斯曼海ODP 1170站位2 Ma以来CaCO3％和MAR-CaCO3的研究发现,CaCO3％以冰期低和间冰期高的“大西洋”型溶解作用旋回为主,并以MIS 34/35期(约1.15 Ma BP)和MIS 14/15期(约0.55 Ma BP)为界线,表现出3种沉积模式.而MAR-CaCO3以MIS 57/58,21/22,13/14和11/12为界表现出“两高三低”5个阶段.CaCO3％与轨道参数ETP和底栖有孔虫δ18O的交叉频谱和小波分析显示,其主导周期明显具有从40 ka向100 ka转变的中更新世气候转型(MPT)特征,转型起始与终止时间为1.15～0.55 MaBP.CaCO3沉积模式的转变与南大洋太平洋区西风带和环南极表层锋面系统的迁移密切相关,在时间上与MPT同步.MPT时期,西风带和环南极表层锋面系统的快速南北迁移,导致CaCO3沉积受到硅质和陆源物质稀释作用的影响.而MAR-CaCO3的阶段性变化主要与南大洋深层环流的变化格局和水团化学性质的变化有关.在1.5～0.85 MaBP期间,南大洋太平洋区深层水通风增强,利于CaCO3的保存和埋藏,MAR-CaCO3增加；在0.85 ～0.55 Ma BP期间,CO32-处于不饱和状态的CDW增强,导致南大洋深部CaCO3溶解作用增强,溶跃面上升,MAR-CaCO3降低.

A CaCO3 Deposition Record During the Last 2 Ma in Southern Tasman Rise of Southern Ocean and Its Responses to the Circulation System and Orbital Cycles

The Southern Ocean CaCO₃ deposition not only records the processes of the biological pump modulating atmospheric CO₂, but also the changes in Southern Ocean surface frontal system and the structure of deep ocean circulation.CaCO₃% and its mass accumulation rate (MAR) changes at Tasman Sea site ODP 1170 during the past 2 Ma indicate a “Atlantic-style” feature with lowCaCO₃% during glacials and high during interglacials. Three sedimentary regimes are presented roughly bounded by MIS 34/35 (1.15 Ma BP) and MIS 14/15 (0.55 Ma BP); and the MAR-CaCO₃ represents five phases fluctuation. Cross-spectrum and wavelet analysis ofCaCO₃% and orbital parameters ETP, and benthic δ¹⁸O records show clear Mid-Pleistocene Transition (MPT) pattern of the main cyclicity transits from 40 ka to 100 ka, from 1.15 to 0.55 Ma BP. The changes inCaCO₃ deposition are closely related to the changes in Southern Westerlies and Antarctic Circumpolar Current（ACC） frontal system, and synchronous with the MPT. During the MPT, the rapid migration of the Southern Westerlies and ACC frontal system resulted in the dilution effect of siliceous deposition and terrigeneous input to theCaCO₃ deposition. The MAR-CaCO₃ variability is related to the changes in deepwater structure and its chemical properties. At 1.5~0.85 Ma BP, Southern Ocean deep water ventilation was enhanced, which favored the preservation ofCaCO₃ and increased the MAR-CaCO₃; at 0.85~0.55 Ma BP, CO^2-₃ depleted Circumpolar Deep Water was enhanced, resulting in the dissolution ofCaCO₃, and the rise of lysocline and decrease of MAR-CaCO_3.