Pleistocene Open Ocean Antarctic Intermediate Water Variability

作为全球温盐环流的一部分，南极中间水(AAIW)不仅重新分配热量和盐分，而且还对中间深处进行通风，并将营养物质从南大洋输送到营养缺乏的热带地区。因此，AAIW对海洋生物地球化学和碳循环具有全球重要性。AAIW的形成本质上与环极地深水(CDW)在南海的上升流有关，并受到西风和与海冰输出和融化有关的季节性清新的调制。虽然AAIW的输送和组成对末次冰川消融期间的海洋和气候变化起到了重要作用，但AAIW的长期变化记录很少。尽管仍有争议，但从大西洋的替代数据中，人们已经开始就上一次冰川盛期期间持续的AAIW流动达成共识，尽管略有减弱。表明更大和更快变化的钕同位素记录已被证明受到沉积叠印的影响，沉积叠印是大多数AAIW深度岩芯被回收的大陆架环境固有的问题。为了避免这种叠印并加深对AAIW长期变化的了解，我们提议进行一项新的研究，利用南大西洋(DSDP站点516)、东南太平洋(ODP站点1236)和塔斯曼海(DSDP站点592和IODP站点U1510)开阔海域的中等水深钻芯。虽然这些地点的沉淀率很低，但初步初步结果表明，已经记录了中间水域预期的冰川/间冰期底栖氧同位素变化的全部幅度，因此其他参数也将是有效的，没有明显的生物扰动影响。从这些含氧沉积物中获得的稀土元素模式将补充海底有孔虫稳定的C&O同位素和痕量金属替代物的温度(Mg/Ca，Li/Mg)和营养含量(Cd/Ca，Ba/Ca)，以及混合有孔虫包衣Nd同位素，作为中深度水团混合的替代。这些工具将有助于重建AAIW的水团来源、AAIW的营养含量和温度演变，跨越大约150万年，涵盖重要的中更新世过渡(MPT)。在每个地点建立了高分辨率的海底同位素地层学之后，将分析从中期冰期之前、期间和之后跨越关键冰期和间冰期的样品，以获得所有替代样品。综上所述，这些来自不同盆地的记录将为AAIW在塑造冰川终止演化方面的潜在作用提供重要的新见解，因为AAIW直接连接南大洋和低纬海洋盆地。在更新世期间，海洋环流如何响应轨道和不断增加的冰盖压力也将获得新的见解。

As part of the global thermohaline circulation Antarctic Intermediate Water (AAIW) not only redistributes heat and salt but also ventilates intermediate depths and transports nutrients from the Southern Ocean (SO) to the nutrient deprived tropics. AAIW is therefore of global importance to marine biogeochemistry and carbon cycling. AAIW formation has been intrinsically tied to the upwelling of Circumpolar Deep Water (CDW) in the SO and has been modulated by westerly winds and a seasonal freshening related to sea ice export and melt. Although it is clear that AAIW transport and composition played an important role for the oceanographic and climatic changes during the last deglaciation there are very few longer records of AAIW variability. Although still debated, a consensus on a persistent, if slightly weaker AAIW flow during the last glacial maximum has started to emerge from proxy data for the Atlantic. Neodymium isotope records that suggested greater and more rapid variability have been shown to be biased by sedimentary overprinting, which is a problem inherent to the continental shelf settings where most AAIW depth cores were recovered. To avoid such overprinting and to develop an understanding of longer term AAIW variability we propose a new study utilising intermediate water depth drill cores from open ocean locations in the South Atlantic (DSDP Site 516), the SE Pacific (ODP Site 1236) and the Tasman Sea (DSDP Site 592 and IODP Site U1510). Although the sedimentation rates at these locations are low, first preliminary results indicate that the full amplitude of glacial/interglacial benthic oxygen isotope variability expected for intermediate waters has been recorded and thus also other parameters will be valid without significant effects of bioturbation. Rare earth element patterns obtained from these oxic sediments will complement benthic foraminiferal stable C & O isotopes and trace metal proxies for temperature (Mg/Ca, Li/Mg) and nutrient content (Cd/Ca, Ba/Ca), as well as mixed foraminiferal coating Nd isotopes as proxy for intermediate depth water mass mixing. These tools will allow the reconstruction of the water mass sources contributing to AAIW, its nutrient content and its temperature evolution, spanning approximately the last 1.5 million years and covering the important mid Pleistocene transition (MPT). After the establishment of a high resolution benthic isotope stratigraphy at each site, samples spanning key glacial and interglacial intervals from before, during and after the MTP will be analysed for all proxies. Taken together, these records from different basins will provide important new insights into the potential role of AAIW in shaping the evolution of glacial terminations given that AAIW directly connects the Southern Ocean with the low latitude ocean basins. New insights will also be gained into how ocean circulation responded to orbital and increasing ice sheet forcing during the Pleistocene.